Last I knew Apex had some NOS stock grips from Wiselite.
Apex have the semi grips minus the AR internals. Wouldn't be hard to use one of them. They list a tall and short type, given the choice I'd go with the tall type which moves the hammer lower in regards to the bolt (which is a common issue on these conversions).
The Wiselite AR style grip is almost the same thing as the BRP, other than it attaches in the front a bit different but if you have not made the cuts on the receiver yet it will not matter. I've used them both and can post pics of the differences if needed.
You could also try contacting Wiselite for a complete grip and bolt carrier. Their B/C uses a two piece FP vs BRP's one piece FP BTW. Again I have used both, both types have plus's and minus, but both work well.