I've searched in google but I can't find where to get a PSU with +/- 12 or 15V?
Current will probably be 2A max.
Do you want to buy one or are you going to build one?
Electronics stores have those, often you can set the regulate voltage and current.
If you are going to make one, there are schematics on the internet and there are firms that sell them as a building kit.
Building a fixed voltage PSU is the easiest because you can use a voltage regulator like 78xx/79xx
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Try mpja.com. Lots of power supplies available with 2,3,4 outputs.
For example
http://www.mpja.com/prodinfo.asp?number=18835+PS
+5, +/-12
try some music shops?
lots of effects units run of sub 2amp +/-12v
KE7GKP:
Back before everything was low-power digital, this was an easy thing to find. But now they seem as rare as hen's teeth and at premium prices. But there are still options. You question is much too broad to offer any practical suggestions.
Do you really need 2A? Will 1A be sufficient? 1A seems much easier to source.
Is this for fixed or portable use?
Do you need something self-contained (like a "brick" that comes with laptop PCs, etc.)? Or an "open frame" type that will be built into the project enclosure?
How "asymmetrical" is the load? Can you use a 24 or 30V supply and a "virtual ground" circuit? Single-ended 24-30 power supplies are quite available and inexpensive.
Too many questions! 
The project is too experimental for me to answer the 1A 2A question, but even so, where should I look?
I could build one myself, but it would not have the certification I'd need.
CrossRoads:
Try mpja.com.
Magic! Many thanks!
KE7GKP:
Here is one possibility that looks much better. Two independent 15V @ 2A outputs which you can connect as +/-15V bipolar.
http://www.alltronics.com/cgi-bin/item/CRM_012GB/41/TDK-CRM-012GB
Alltronics are selling (likely surplus) units for $25.99 Enclosed cage suitable for putting inside the project enclosure.
Datasheet: http://www.datasheetarchive.com/dl/Datasheets-35/DSA-698496.pdf
Many thanks!
By the way how did you find them? I googled and googled, but obviously with the wrong search terms...!
A good google keyword here is "dual-tracking".
I've bought lots of stuff from them before 
They send out catalogs too, lots of neat stuff.