I know this is an old post, but if anyone else pops for amphetamine, a good excuse is the medicine Bupropion, it's available as an anti-depressant called Wellbutrin. Even easier to get is the Bupropion+Naltrexone combo for "management of chronic obesity" or smoking cessation, brand-named MySimba.
@MadHatter
Nitroethane and Nitromethane are both used in RC models in "nitro engines", it's something about little cars or whatever the ***** they are that people race, apparently they look for that boost (apparently it destroys the engine over time though?), the actual fuel is apparently used in models of scale 5:1 or bigger. Best bet would be to find a place that you can race those things at and take it up as a hobby, I bet it's just like with bullets in Europe.. you might not have a permit, but if you belong to a shooting club it's no problem to get a case... Nitroethane I have seen listed on the brand-name NIPRON as a fuel-additive AND also as an engine-cleaner and descaling agent.. most nitro compounds could be used as solvents for whatever weird reason I assume..
@Methylamine
Pesticide manufacture.. Manufacture of NMP solvent... Multiple agricultural uses..
Methylamine by itself might be a tough one. Depending on the solvent you use to dissolve methylamine, you get a different compound, so if I was you then I would see what solutions of methylamine are called and then what they are used for, you'd probably get a much bigger list that way and be able to pick yourself an excuse from there much easier.