Fuses for an old Chevy?

I can't seem to find a store that carries the big ol' glass barrel fuses that fit in my 66 Chevy Impala.. I recently swapped out my 283 for a 350 and I'd like to update its electronics a little bit so I can get more juice out of the old girl.

Any help or common knowledge would be appreciated.. btw I searched classic industries and advance auto parts and they don't seem to have what i need. or at least their search engine SAYS those fuses won't fit my car.. i'm too afraid to take out the old fuses to take into the store to compare them since they're glass and probably pretty fragile.