Hello and a Request For Help Please!

If the dealers you ask don't stock Pentax (or some other camera you're asking about) of course they're going to try and sell you something they do have. If they'd had a K-50 or similar surely they'd have wanted to sell you it, sounds like they'd have been glad to get rid of it. I don't think it is Pentax (or Ricoh now) who bribe the magazines for rave reviews, we often think how underwhelming the advertising is for Pentax products compared to the others. If a Pentax does get a rave review it is more likely the reviewer has been genuinely surprised.
Often Pentax get criticized for their camera menu systems because they are apparently different to the other makes. But Pentax try and retain some consistency across the range; the menu system on their DSLRs is much the same as on compact and bridge cameras, Having used a Canon EOS I can state that the Pentax system, to my mind, is much more straight forward and quicker to access the function you want (and that works across the range.)

As for lenses, there's plenty around if you go to the right shops. There's a good range of current glass plus all the legacy glass going back decades.

Both SRS in the UK and B&H in the States would offer an unbiased recommendation as they stock the other makes you mention too. Other dealers do sell Pentax kit too but they're not nearly as widespread as the big players.

While some time ago Pentax DSLRs might have seemed pricey compared to the competition that isn't the case now for a solid, well made camera. For your intended subjects the Pentax would be ideal. A quick Google for the K-50 shows pages of 5 star reviews from all manner of review sites and blogs. Surely they can't all be wrong!?

By all means choose Pentax for landscape or architecture but I suggest you search for posts referring to tracking autofocus. For moving railway photography I find more consistent results by pre-focussing on a certain point instead of letting continuous-AF do its own thing.

Back Button focussing is also a useful technique to learn, basically it means keeping your thumb on the AF button, which then continuously focusses on the subject, and your finger on the shutter release, since I learned and remember to use this technique, I've got much better images of birds in flight and even fast moving aircraft.

GBR - where are you based?

Re. Lenses, Ricoh claim on their website that they have more APS-C lenses available than any other manufacturer; Canon and Nikon have a wide range as well but most are in the FF format aren't they? I wonder how much disinformation is disseminated to store staff by camera reps. Also, try listing how many of the other make's lenses are both WR and have IS - it is surprising how the choice reduces down.

The one thing that no one has said yet is that Canons and Nikons weigh a ton by comparison to a Pentax. I was handed a very expensive Canon recently to photograph its owner and his family and even knowing their weight I was still surprised. Lug one around by all means. I'll stick to my K5!

As most dealers don't stock Pentax equipment they're most unlikely to recommend them over the more popular Canons and Nikons. They won't give unbiased advice because they need to sell what they stock.

You'd be better off reading as much as you can on-line. There's so many reviews out there and lots of YouTube videos where you can see the equipment being used.

I'd not worry about the lack of lenses for the kind of photography you're interested in. There are plenty of new and old lenses which will work on Pentax bodies.

You might do well to start with a reasonably priced second hand body and a kit lens (18-55) to see how you get on, there are plenty to be had on the market. A lightly used K5 would be a good choice. Then, if you like the camera, you could perhaps buy something like a K3 or even K1 further down the line.

I'd not miss the opportunity to test one of the new mirrorless cameras made by Panasonic, Fuji, Olympus and Sony. They tend to be smaller and lighter, as do the lenses and, as you're used to an electronic viewfinder, they may suit you.

You're in a good position not having yet bought into any one system and these days it's very hard to buy a bad camera. Most of the lads on here would take great pictures with anything being sold at the moment.

There are good Pentax dealers around with displays, in no particular order here are a few:
SRS Microsystems
Clifton Cameras
Wex Photographic
Cardiff & Newport Camera Centres
Park Cameras
LCE Gloucester
Harrison's Cameras
Bristol Cameras