There are AT to PS/2 converters, you just need to find one on E-Bay or somewhere.
I'd try and get some keyboards the same way, i.e. landing bargains as they come on whatever keyboards those are from your demand range and your price range, particularly if you can save some on shipment. I currently have almost 20 keyboards here for this reason. Still haven't arrived at my favourite yet, though. BS the loveliest but too stiff, scissors too rubbery, Alps too wobbly, black Cherries too unpredictable/strange to type on, brown cherries hard not to bottom out (plus I broke the contact in the spacebar when mounting the switch back late at night and tired) etc. etc. Plus, it's kinda fun looking for bargains and being surprised.
If I had to sit down and spam some code, I'd probably pick either Model M (the general favourite but really largely because of the emotional attachment because this is the same unit I had as a teenager) or the least wobbly Dell out of the 10 in my collection. Brown Cherries might be too light when going through the punctuation cluster (brackets, semicolons etc.). I'm not sure because I've never touched one, but blue Cherry could be the best switch for coding jobs, at least judging by my taste (clear tacticle actuation, medium strength), although I'd be tempted to keep experimenting.
What would be even better would be getting this 3178 terminal keyboard plugged. That's the best typing feel I've ever had. Perhaps Model F would be the closest thing to it out of what's normally operable with a modern computer.
Besides, people claim Model M's differ between one another (I would say the Dell AT101W's also do...), so if you live in the US, where you can find them at flea markets and similar places, then you could take a walk from time to time and just try by hand if that's what you like.