Yes, you can use the canting beds from the 390 Boss. This was discussed recently, the difficulty is finding the beds separately. Apparently Rome doesn't sell them separately, so you'll have to try sourcing them from someone with 390 Boss bindings who doesn't need them and is willing to sell.
A question that I have, that can probably be easily answered by a trip to my local shop or an email to Rome, are 390 Boss beds and Targa beds the same/interchangeable? If yes, it should make finding Rome canting beds a little easier.