Literally every drug store will have it, and many grocery stores will sell it to, it's not like isopropyl(rubbing alcohol) is a controlled substance, just get a bottle of it, there are no good substitutes except maybe moonshine.
Just use about a 90% Isopropyl Alcohol with zero additives beside sterile water!
Didn't think so so thanks for confirming that
I don't have any isopropyl anywhere so is there anything I could use as a substitute that would be safe?
I would just wait and snag some when you can, it only cost about a US dollar amount of money, because you're not in dire straits, you can always wait and get the proper stuff, you do not want to use anything that leaves a residue behind that could react with or compromise the integrity of the new thermal compound.
Denatured alcohol (methylated ethanol) or Everclear (pure grain ethanol) work fine too (ironically pure grain ethanol can be hard to find in some places). If you don't have either of those, then get the isopropyl and make sure it is as pure as possible and don't use the kind that is scented or colored.