Hi Bp,

I am also self-employed.
I asked one of my client, the president of a company I often work with (which could also be a supplier in your case), and my mentor/advisor (somebody that did an mba and started a business also).
In my case I never had a supervisor so it was even harder than you, I think a client and your former supervisor should be good, use the mentor as a third one if you need it.

Cheers,
A.