Are You just talking about eliminating a counter pulley setup, or are You saying you want to do away with pullies and belt all together, and go to some kind of gear driven setup? I'm trying to picture what You mean. I guess a source for motors may depend on what kind you want, but there are many places on the web for surpluss motors, like Surpluss Center for example. I would recomend a google search. I've been looking at blowers with them lately, and there are more places then I can count that come up in a google search. There were sources for both new and used.
Shipping can be kind of high on the motors, as they weigh alot, so a local motor works may be a better choice. I'm waiting on shipping, but I just purchased a belt driven blower, and It was alot cheaper to ship without the motor. I have a 1/2hp motor with a craftsman label (made By someone else I'm sure) It has a triple stepdown pulley setup, and I may use that. Anyway I bought that motor some time ago as an extra lathe motor, and even back then I paid a pretty penny for shipping. Anyway I've seen some blower & fan motors that are basically the same thing. I think they are around 1725 rpm's.
I don't know what it would take to run a lathe like yours, and i guess it would also depend on if you wanted variable speed, but not mentioning any names, some lathes use a fan motor, and some can be wired in a 3 or 4spd configuration I believe.
There is also usually a good selection of motors on ebay.
There's probably some good articles online for doing the conversion You want. There seems to be sites on just about everything else these days. I learned alot about the different styles of spray booths I could build, and the in's and outs of each one, which was a good thing, because one style I was gonna do can cause some problems with dust getting in the finish, and that was something that I hadn't considered. You can also pull too much air which I wasn't aware of.
Wish I could be of more help, I'm sure there are people here that know alot more about the conversion then I do, hopefully you get the info Your looking for. Good Luck with it.
Greg