dts CDs have long been discontinued; possibly 5 years or more. They were more or less dropped in favor of DVD-A, and now that DVD-A is all but non existent as well, sources for either are going to be slim. Same story with SACD. In the last year, production of any mainstream titles has dropped off significantly.
All dts capable DVD players can play dts CDs, as well as most standard CD players with digital out. No Sony player can play DVD-As.
For the PS3, IIRC, there are only a few models that can play SACD - the original launch 60G for sure, and possibly the subsequent 80G not sure about the 40G, but none of the Slim models can for sure.
Amazon, eBay, etc... are going to be the places to find them and expect to pay top dollar for popular titles that have been discontinued. For those titles that are highly sought after, prices are very steep.
You can order most of the Porcupine Tree DVD-As at burning shed. These are excellent discs that I would not hesitate to own and they are at normal prices.
http://www.burningshed.com/store/porcupinetree/ *edit - I just looked and a few of the discs are not available or out of stock, but the recent releases are all there.