I havn't added the Promaster section yet because I frankly havn't had the time, but most of the places that sell stuff for BKO's and B2K's have promaster stuff since most is interhcangeable.
Theres no real reason to buy a new board for Promaster's unless its the last upgrade.
Better upgrades are, the ICDU LP Ram, new valve, new reg, and a new LPR. If you replace all those, it will be shooting just like, if better, than an ego.