NHCl2 (dichloramine) is not used for making MeNH2 (methyamine). I assume you meant ammonium chloride, which is NH4Cl. Remember that you need formaldehyde as well, and that's not particularly easy to come by. ScienceMaddness.org has a document on it in their library, though I don't know whether the method works or not. In SWIM's experience, the hexamine method detailed on Rhodium's page works very well with hexamine camp fuel tablets. Note that 500g might not be all that much. Ammonium persulfate has a formula of (NH4)2SO6, so that's only ~22% NH4 ions / weight. Less if the substance is sold as a hydrate (likely). Seriously, 5lb (NH4)2CO3 (37% NH4 ions) is only about $35 if you search a bit, and can be used directly with muriatic acid, without mucking around with reducing the peroxysulphuric ions, then precipitating, etc.