In the current patch to get to the bunker you need the punctured card, vit you can only get it in convoys, heli crashs and in toxic zones, all off them have better weapons than in the bunker.
Making it it only one use would be a great idea, and only found in toxic zones. Also putting a chance of spawn on the third level of the bunker the Fal/Svd/Lemas instead of the aug, would incourage more players to go there.
Using a battery to open the bunker from inside is another solution to the players that keeps farming it nonstop.
And adding a airduct to get out off level 3 to level 1 or the stairs in a way that you cant get in from it would help solo players too.