tm hi-capa 4.3 gas?
 

which gas should use for my hi-capa 4.3, and where can i buy it?

I vote you pop over to airsoft parts and pick up one of these.
http://www.airsoftparts.ca/store2/in...roducts_id=715

Its an adapter package that will let you use propane or computer duster gas to power your guns. The coleman cans will fit the larger adapter and the smaller one is for computer duster spray. Just a note it has been noted that you should avoid duster gasses with petrolium distilates in them as they have been known to damage orings.

Duster gas would be appropriate for your gun, however I have heard that the newer TM Hi capas (Im assuming your hi capa is TM) can run propane safely out of the box. However I cannot confirm that, hopefully someone else can.
I hope that answers all your questions.

Tm Hi-cappa's run propane fine. I had a 4.3 ran it on propane for 2 years, currently have a 5.1 and no porblems at all.