Sorry, but magnesium ribbon is not going to reduce harmine (at least I very strongly suspect not).
For any chance of a successful reduction using magnesium, you'd likely need to use fresh turnings and maybe even a completely inert atmosphere like argon. Unlike sodium oxide, magnesium oxide is not dissolved by alcohol. This oxide layer will prevent magnesium from reacting.
Another trick to try is adding a crystal of iodine to the magnesium when it's in the alcohol. Once the brown colour disappears from the solution you could add the harmine. [Iodine is also rather hard to get these days but not beyond the reach of sufficiently resourceful people who are prepared to go to some lengths to isolate it if necessary.]
Methanol is a better solvent than isopropanol for harmalas and may also be a bit better at providing protons to the reduction reaction. It all does boil down to availability of materials, of course.
Raney nickel was mentioned above, but use of pressurised hydrogen is rather an advanced technique and decidedly hazardous - besides the explosion risk of hydrogen, the catalyst itelf is pyrophoric. Urushibara nickel might be worth looking at for this reaction since it is all-round a friendlier material to prepare and work with. Its mode of preparation can be selected to optimise the type of reduction for which it will be used. That subject is its very own rabbit-hole but if you decide to look there you'd best search with the aim of reducing a substituted pyridine since β-carbolines are a bit niche.
This is all leading me to a logical conclusion that you might as well first of all try using your magnesium ribbon to reduce a harmine salt in acidic water. If that doesn't work, your next easiest option might be to crack open a lithium battery. Again, a significant degree more dangerous and with numerous additional caveats.