Darkgael is correct, in that a Colonel..or a Sergeant or PFC for that matter, cannot just go to the hardware and purchase a hammer, unless he wants to pay for it himself..
That being said, just that method is often employed. Back in1957, I was serving in Ft Sam Houston, in a company that had extensive lawns.
The army would only issue a non powered push mower, so at payday each troop was asked to kick in a dollar to get a power mower.
That was done often..
We often bought stuff overseas, for items the government doesn't furnish..after all we troops didn't have limitless credit cards, as some politicians do.
No reason why parts and tools should not be so costly....except somebody is getting a kick back..
Yes, the government has procurement offices, and they should be doing a much better job..or the personel should forced to explain why a hundred plain washers should cost $90,000... or be replaced. Or perhaps the person who ordered the costly washers, should have their pay docked for the $90K..and/or go to jail..
Procurement in private industry means.."getting the best quantity and quality you can get, for as few dollars as possible." Bureauocrats are either blind or crooked.
https://www.youtube.com/watch?v=0CvKcIvovIQ