We have thin grips on 4 of our 1911s, three of which have ambi safeties. They are all CMC and we like them.
If you are not particular or too particular about color, the cheapest place I have seen them is through www.natchezss.com . Their price right now is $41.03 which is hugely cheaper than from CMC. Go to the web site and search for the words "slim grip" and you will find CMC's stuff.