Digital BW, The Print

I've somehow misplaced the little rubber caps that came with my 
refillables, and have had to resort to things like duct tape or hot 
glue, neither of which seem to get a complete seal.  I'm tired of 
perfectly good prints having ink leaked all over them.

Anyone know where I can pick up some caps that will fit these carts?  
MIS says that can't get them seperately, and don't know when they'll be 
able to.  So I'm looking for another option.

Thanks for any input.