well there are a few local retailers that carry some of that stuff.
http://www.airsoftparts.ca carries most of that stuff, and it's in country already so you won't have to wait weeks to get your parts. And illusion, here on the forums sells a bunch of TM parts that would work, he can also do some custom orders if you can't find what you need. Or you can try international retailers...
red wolf is popular, and so is WGC shop and E hobby.
There are tons of stores that carry all that stuff, it's all fairly common. You just have to do a little bit of research to find out if some parts might be better than others. Most of the shops all sell the same stuff and all for around the same price.
Some brands are better than others. Some cost a lot more than others.
I am currently using an aluminum Shooter's Design slide on my G17 with an extended inner barrel and threaded outer barrel. It works great but it took a bit of work to make it cycle nicely. Some slides work great out of the box, some require a bit of work to make it work better.
If you use duster gas, you'll shoot 270 FPS, if you use propane you'll get closer to 300 FPS, but if you're using propane you will want to upgrade the slide so it doesn't crack.
Upgrade the loading nozzle for the added strain and power output, and same with the steel sights. The sights are used to hold the blowback unit in place in the slide, and the added power of the propane will cause it to break, so you need to put something in there that's going to withstand the pressures of a propane powered gun.