Large production runs (think cars) the tooling is sold to a third party to make spare parts. However that third party will watch what sells and scrape the tooling when sales are not large enough to justify keeping it around. Things that never break have the tooling scrapped early. Things that collectors break the tooling stays around - if it wears out they make replacement tooling.

The SR-71 was not made in large enough numbers to get the above treatment. If the government wants spare parts they need to pay to keep that tooling around.