Have a grinder and cut-off disc? You can make more thread chasers than you'll ever need using the old bolts. Use the cut-off disc to make a slot or two: Or, if you have a flap disc, you could just grind some simple flats into it: Or, if you don't have a grinder, use a hacksaw to make a couple thin slots (I'd invest even in a HF grinder before doing it this way): Have an air compressor? I like to use a blow gun with a 12" needle tip to blow out the threads starting from the bottom. Squirt a little brake cleaner in the hole, brush it with a thin nylon bottle brush, then blow it out. Wear side-shielded safety glasses!