The hammer and toilet seat incidents make for a lot of laughs but here is how it works, and I am not defending scams and corruption. Virtually all spare parts for a military system are put forth as a package.
Those parts have to meet certain specs and many are unique to a military vehicle or aircraft and key point: they won't work/fit in a civilian setting. The package is part of the bid, and if accepted, the huge amount of nuts, bolts, circuit cards, toilet seats, and hammers are priced out. We had $4.00 bolts for motor mounts which in 1980 is ridiculous to the layman, but all parts must add up to the agreed price of the package. And at least in my day, they were all accounted for and came out of the unit's operations and maintenance budget, so it behooved the commander to watch his $$$ carefully.
For the 211+ trillion unaccounted for in Pentagon assets, I'd start looking at the Taliban. Maybe they can give us a count.