Loaders are pretty specific to a given tractor or series of tractors (example: the 430 Deere Loader fit the 4200, 4300, 4400, 4210, 4310 and 4410..plus a couple other models (in fact, I'm not sure the 430 loader would fit the 4200 and 4210 since they have a shorter wheel base).
So, it's not like you buy a loader off Craigslist. You really need to know it it's at all compatible.
If the loaders you saw are aftermarket, you could contact the manufacturers of those loaders.
It's also going to depend on how good you are at fabrication and assembly. It's possible you may have to fabricate the mounts.
You really want to do some homework and research before you buy any loader. Not saying it can't be done...just know what you're getting into.