http://stores.ebay.com.au/learcnc - Ben's pretty helpful . You'll not get 150x150 neat, but he has 140x150.
http://www.ebay.com.au/itm/LearCNC-140x … 2ec9083bdb
Jamie from 3DPrinterGear up in the Sunshine State does the 200x200 and 220x220 sizes.. and he might be able to source a smaller sheet... but given the rarity of 150x150 printers, don't hold your breath on him having it ready to send...
Theres many many options on fleabay, including local-shippers... Just look for Borosilicate Glass :
http://www.ebay.com.au/sch/i.html?_from … mp;_ipg=50
Just remember, all glass is not alike... and the majority of people that champion just using framing glass end up with broken bits from thermal stress or head crashing... Borosillicate (or, as you may know it in the Kitchen, "Pyrex") is tempered and thus 'hardened' glass (except on the edges, where it will chip but not shatter) and is designed to be taken to high temps repetitively... consequently... whilst it might cost $15, you'll not need to replace it due to heat cycles or 'whoopsies'.