Welcome to PU.
As Tamron have been making the Pentax lenses lately, if you want a Tamron, get a Pentax! Why would Tamron release a duplicate lens if it contravened an exclusivity agreement and jeopardise future releases?
I can't see that Pentax lenses are overpriced in comparison to their Canikon equivalents, do you have any evidence of that?
If you want third party lenses, look to some of the other manufacturers such as Samyang and Irix who produce lenses with a limited appeal such as their extreme wide angles.
Which lens/lenses apart from that lensbaby (and I'm sure you'll find one if you look) are you not able to obtain in K mount? Also, are we talking APS-C or full frame? If the later consider that Pentax were late to the Full Frame party but have new releases on their road map.
I'm sure Sigma are watching the market and if they feel there is commercial value in releasing K mount versions they will. for them, though, the process is more complex as the mount is quite different to Canikon. Maybe the PLM method (which is closer) will help we'll have to see, but that is a pretty new development and not supported in older Pentax's and maybe Sigma won't want to spend any money licensing it (as per usual.)
Given the wealth of fully compatible old glass along with current offerings from the Pentax stable, I can't think of any focal length that isn't available to use on a K-1 already. I really must ask again, what do you feel is missing?
If you just want something cheap to fit a Pentax, there's plenty of choice from the likes of Vivitar, Soligor, Tokina etc. availalble. While many will be second-hand, they can still be found often in mint condition at rock bottom prices in dealers and auction sites.
No, I can't agree that there is a lack of K mount glass available on the market today. As a collector, I might think totally the opposite!

A light box? Far too high tech. Hold the negs up against the sky to view them!

You don't have to use it that way (we've discussed that before.)

A suggestion, turn off the orientation in the camera then that rotate command won't be created. You'll also see the full image on the rear screen too. Then having got your image use windows explorer to rotate it. Also Irfanview is a handy program for manipulating an image's, size, orientation, adding borders etc.

At the end of the day, whatever is creating that rotate command, use something else. I know you don't like to manipulate your photos in software but using basic commands won't alter the colour, exposure and so on without you asking it to!

A little investigation suggests the site isn't acting on the Rotate 90 instruction in the exif when images are incorporated into a thread. One for the site developers to investigate perhaps as they really ought to come out the right way up.

To avoid the issue, rotate the image in some other software which actually rotates the mage and resaves it with both correct orientation and exif data. But that is a workaround as technically the files are valid to show correctly as proved in the full size view which takes the orientation instruction into account.

Suggest you check the date of JW's post and the date of his last login! (Save you the trouble, it was in 2016.)

There's some examples here: https://www.dpreview.com/forums/post/58315474
You'll note there is a tiny bit of vignetting and softness in the corners, but not bad at all unless those aspects are important.

Nothing to stop Pentax users creating stacked images as we all know, just not in camera.
This website by PU member nass explains all.
And this thread on the US forum may also be of interest

Sorry to hear people think their current APS-C cameras no longer cut the mustard and that Ricoh have gone all full frame. For those of us wanting FF I think we waited for an awful long time for that to arrive in the meantime seeing many APS-C models come and go. Are people really that desperate to buy another APS--C offering? What do people think it will do that the K-3 or KP can't already?
Just to point out that the K-1 can be set for APS-C use too, but why would you?

Thanks Chris. I hadn't missed it then!

I must admit I've given up browsing there when I regularly did previously. It used to be simple to see what they had of interest but now it requires too much effort to make me bother. I had bookmarks for each of their lists so only had to click on each in time to see if anything had turned up of interest.
Maybe they needed the updated site to help with VAT automation or something, but they really need to bring back the way it worked before.