I hear you... I was a chapter founder also. There were 10 of us when we first became a colony, and nationals said we would get our charter when we had 25 members. After some COB'ing and a good fall rush, we had 22 members - and the fact that we'd more than doubled our membership, plus the fact that we pulled off an awesome fundraiser, impressed nationals enough that we were chartered anyway.
So don't take that 50 as a hard and fast rule... a good rush or two and you will be well on your way.
(Though I will admit that our "pain" was lessened by the fact that the 10 of us were initiated in the spring - we didn't have to wait to be chartered...
)