REALBASIC allows the porting of PC VB code to a universal code that can work on Mac, PC, and Linux. REALBASIC allows the hooking into the completely different API (application protocol interface) that these three major operating systems offer. REALBASIC's porting guide from VB to their system is here:
However, Visual Basic itself doesn not work natively on a Mac.
The barrier to entry to do these conversions are:
A)Almost all of the VB frontends are closed source
B)Its $500 for the professional licence. The academic is $419.30. This does not even include the subscriptions to stay up-to-date.
Anybody that wanted to do this conversion would have to charge $$ to help fund it or take a hit in the wallet.