Kevin,
I while back I was in Wallyworld and came across a "Yoga" block for under $12.00 and this stuff is dense and you can get quite a few quiver foam replacements out of the 2 pack...Search it on line and some are 4" thick...cut with bandsaw,hacksaw,mitersaw,use a rasp,foam sanding block,belt sander,or bench sander and shape it till it fits inside..Plumbers goop from Lowe's or anywhere will hold it like it's there for life...Plumbers goop is waterproof comes in a purple tube and I use it to hold many leather products..You can even use the Yoga block for back quivers, filling that worn out vital section in the 3-D targets or any 18-1 rinehart target cause it actually feels like the same material..I wrote about these blocks a while back here and a few members have tried them and was amazed...Just go in the sporting goods section and look for a rectangler block ... You will be amazed I guarentee...
Keefers <><