fyi - Out of the box, SKU search will work on the advanced search page if you check off "Search In product descriptions"
I found a quirk with what your statement above. YES, that works if there is only one SKU for that product. But if there are more than one SKU for that product, then it dont work. (unless you entered the SKU in the description manually)
I need to figure out how to do SKU searching on my site. :( Note: I dont do code in VS. Or do I have VS.
I can search by Sku on my 3.30 test site? But I have NOP Templates Ajax Filter installed so that probably has something to do with it. They have a free trial version you could test it .