Source for "hobby" guns

[TCups]

Where is the cheapest place to acquire a couple of "raw" Chinese air rifles, both a CO2 and springer model, for the sole purpose of completely disassembling and re-assembling them, learning the basic operation of the mechanisms and teaching myself a bit about routine maintenance and simple modifications.  Which models are the best for this purpose - ie, readily available parts and the potential to end up with a decent shooter?  Thanks.

[SirNomad]

rexdist.com has the springer models. I'm actually planning on ordering some from them for this purpose....just the $100 minimum orders