Ten splines? Might be Redline compatible spindle. Might be proprietary to that particular model of crank, too. Shouldn't be a big deal. if you don't need to replace the spindle or arms.

I agree that it looks like a European bottom bracket. BMX doesn't generally sell the spindles with the bottom brackets, so you need to find out what the spindle diameter is. Should be either 19, 20, or 22 millimeter. 20mm isn't very common, that I've seen.