So I just bought a 1991 MR2 GT turbo with the 3S-GTE engine producing 165kw. 
It's pretty stock at the moment, and I don't know how to fit a boost gauge (Can you put any type on?). 
Does anyone have a good website I can use to do this?
Also, will any eBay boost gauge be suitable?
Cheers!

I'd recommend either the Omori gauge or the EMSpowered unit. Both will mount in the instrument cluster easily and have guides for installation available, but the Omori is analogue and the EMS is digital.

If ordering the Omori make sure that they have the older style, the newer ones they produce don't suit SW that well.
 
http://www.mr2australia.c./mr2play/tm.aspx?m=89967
 
EMSPowered? Maybe if you can find one here already, I think Totenkopf may have one for sale. EMSPowered (Baktash?) has an awful reputation in delivering the goods.

I've heard terrible things about EMS as well, but I took the chance and had it delivered within a week. I might be hesitant to buy something that requires manufacture, but for the gauge I'd happily use him again.
If you want a digital gauge, it really is a fantastic product.

Stay away from Ebay gauges if you can afford it. Unless it is a brand name of course.
Their accuracy can vary greatly which is not what you want when your turning up the boost :) 

I use an Auber instruments digital boost guage hooked up to a GM MAP sensor, installed myself. It has a PEAK hold function and programmable "over boost" alarm/LED too which is handy. I didnt like hacking up my stock dash. Might not be everyones cup of tea but works for me.