Without wishes your options are finite. I'm not sure if random monster generation still occurs at D50, I think not. Summon monsters could be an intermediary means.
If you can find a way to damage monsters without incurring chaotic alignment, you can also heal them for lawful boost, even with crude means such as throwing potions of healing at them. Wands of trap creation may be useful here as well.
Check for potions of exchange, they can offer potential for obtaining other items of the same type.
If you're still not L+ after clearing d50, then you must nevertheless be pretty close, maybe this is within reach.
"Hell is empty and all the devils are here."