If you don't wanna buy trains then the only other option is to join the edu starting job and use JP there to gain int (or w/e other working stat you want), some comps will rotate trains for free but depending on the type and star rating of the comp you might only get a few trains per week (and youll need to double check with the director to see if they're willing to swap your position to an int one for traininy, though most are)
The downside of education ofc is you're essentially "wasting" or giving up your company slot for work stats only (the pay is negligible, and there's no other perks to be had) so if you go that route make sure to have a plan on when to leave and join a more beneficial comp for perks or pay eventually