Anyone know where to purchase the 3.5"x3.5"x1 1/4" (80mm I believe) white plastic case fan mounts that hold the fan in place, have looked all over, but there doesnt seem to be anyone that stocks them?
Thank you.

You mean for a front case fan? If so, I never paid a whole lot of attention to those but I am thinking they may be propietory. If you only need one or two check with a computer store that has old junkers laying around.

Yeah, its for a front case fan, thought that there would be a surplus somewhere for sale, but I guess not.

What is the correct term for this item btw?

I believe that is called a fan cage. So it would be fan cage for front case fan. As I stated, I don't think they are interchangable. Front case fans are of questionable value anyway. If you install a low volume fan in the front it can actually impede the flow of air. Read case fan/s are all that is really needed. Mod the case and install a quiet 120MM rear fan pushing out the rear of course. Put a guard on it to protect fingers when you forget the fan is running and reach back there. Vendors that sell fans also sell grills. Cut all metal away and then use a wire grill. If you can get a 120 in there then use a 92MM or an 80MM. For your info; 1 inch = 25.4MM.

i have the same problem - my case takes a bottom front 80 mm intake fan and a rear 120 mm exhaust fan. there are screw holes for the 120mm fan but nothing to hold the 80 mm fan in place. i have looked all over for a mount or bracket of some kind - even e-mailed the case manufacturer - without success. hard to believe that the intake airflow would cause any problem...

Believe me it can cause restriction under the right circumstances. The front intake is already restricted. If you further block it with a smaller fan than the discharge fan you will cause negative pressure in the case. Remember the PSU is also trying to get air from the front.