Belloborn and Keonslings do them.
Hippababy (in NZ) also does them, although I'm not sure if she is taking on more work or not at the moment - but I know she will do it if you go through tinoki.
If you don't already have a specific wrap in mind to be converted, girasol RS's are a good option (you an buy them off ebay or through tinoki) as they are already converted for you.

Having said that, it is really easy to onvert them yourself. All you need is some suitable rings (which most of the vendors stock or can get in) and some durable thread sewn with at least three lines of stitching.
Thanks misty. My Lenny lamb (what I want converted) is really long so I wouldn't even know where to start to do it on my own!

I was originally just going to sell it but it has some sentimental value being my first wrap lol even though I barely used it