Before I start with substitutions for KBr: have you asked a local pharmacy whether they stock it? They won't match Formulary's pricing, but the DS-15 recipe doesn't ask for large quantities anyway.
Assuming you have access to other raw chemicals: every restrainer will do. You can use Benzotriazole, Sodium Bromide (as suggested by PE), Nitrobenzimidazole, ... be careful with strong restrainers like Iodide or Phenylmercaptotetrazole, though!
Assuming you have no extra raw chemicals: leave out the Bromide and see what happens. If you get fog, try to lower pH. Acetic Acid works nicely for this purpose, Sodium Metabisulfite may be in your chem stash somewhere, and you can add more Salicylic Acid or Ascorbic Acid (which you have anyway if you mix DS-15). Even Citric Acid or Bicarbonate will work. Start with small amounts and process tiny test clips. Incrementally add acid until you no longer get fog on your test clips.