The US normally wouldn’t send Ukraine anything except weapons that are not critical to national defense. The Javelins being sent might be close to needing upgrades, refurbishment, or otherwise cost the government so money to keep them in service.
But according to US Army contract, the production has been 37,739 since production began in 1994. Every year, U.S. forces use some missiles for training and testing. Thus, there may be 20,000 to 25,000 remaining in the stockpiles. These 7,000 systems sent to Ukraine represent about one-third of the U.S. total inventory.
The production rate of Javelin is about 6,500 per year. That’s not a lot in terms of the supply of chips needed to produce them, but all it takes is one part that in short supply to slow or halt production. The government does have authority to force supplies to move to head of the line for critical defense items.
A mix that includes the Carl Gustav recoiless gun might be needed if this war continues – and they are much less expensive as well.