You
might be able to get away with either boiling xtra long, or possibly microwaving (depending on what kind of container your using)
Why can't you get a pressure cooker? Just curious...
You can colonize at decent room temp, but it will take longer. Ideally you want about 84-86 degrees. I've heard on top of the refrigerator is a good spot. Keep 'em in the dark.
If you haven't already - check out shroomery.org. Like this site is for pot, it is for shrooms.
I started my first grow a 10 days ago, got a bunch of jars about half colonized!
I used a pressure cooker - no contamination so far.