So far this year I've acquired two pre-lock 617's, a no-dash 6 incher and a -1 "4 gun. They weren't cheap; I paid $600 for the 4 inch gun and $550 for the 6 inch gun.
They're wonderful revolvers. I suspect that, if you keep looking, you'll find one. There were a couple of them for sale on Gunbroker within the last two weeks.
Personally, the lock means nothing to me. If I were still in the market, I wouldn't care about it one way or the other. What I really like about the pre-lock models, however, is that they are both 6-shot guns. That suits my interests perfectly. I was uninterested in the 10-shot models because, frankly, 22s are a huge pain in the butt to clean, and the thought of cleaning a 10-shot cylinder makes me gag.
That's also why I'd keep looking for that stainless model, btw. Every time I clean my 617s (usually, after each trip to the range) I wind up scrubbing vigorously with bronze wool to get the carbon fouling off the area around the forcing cone, the top strap, and the cylinder face. No way that a blued finish would stand up to the elbow grease that I find necessary to keep these guns clean. On the other hand, after cleaning, the stainless finish remains pristine.
Good luck with your search!