Third Party Softboxes for Einsteins

I own several Paul C Buff softboxes and their great, but I need some sizes that he does not make.

Does anyone know where I can find a speedring that will fit the Einsteins, and can be used with other brands of softboxes? The speedring is the "balcor" type.

Help is appreciated!

bowens quick ring with balcar insert. I use photoflex SB's.

there's a few really good threads about this ring here on POTN - http://www.kaceyenterp​rises.com/?page_id=481

It's been a long while since I posted this thread and here's what's up. I'm still using PCB Einsteins, although I also have an Elinchrom Ranger kit now. I have found tons of third party options for PCB soft boxes, most notably the Fotodiox brand. Very inexpensive and good quality.

I"m very pleased with these options and it's kept me sticking with Einsteins as my primary studio setup. Thanks to those who responded to this post!

Thanks for the update. I have a set of 4 Einsteins and I'm reluctant to use off brand speedrings because the spring clips with the Balcar mount can be finicky.