Well, 200k Luna could buy you a 3*. 4* are way more expensive, and you could buy one or more with either 1 TE/Potion or 3 goddesses.
Doing the Mina trials would give you a 4+ ticket, which allows you to get a 4* or better card, fulfilling your needs. These also appear from time to time in daily roullettes, at the rate of 2 per month iirc.
Also, premium tickets are easier to get and give 2* and up, so getting a 3* from a premium ticket is quite possible.
If you're having troubles with finding one regardless, I'll make you a one-time help: I'll trade you a 3* and a 4* for 200K luna. The cards are of my choosing, but i promise i won't choose the worst of cards for your starter case.
1 - you need to be level 30 to make any sort of trades;
2 - you have to wait until this event is over, because it is disabling trading;
3- you'll have to make the first contact and remind me of whom you were, as i won't be looking for you once the trade lock is over (hint: use my ID number on your search);
4 (off-topic, but it matters) - if you want to do another trade request or open a trade service, you'll have to edit this thread, or contact a moderator and ask for help in deleting this one once you're done with it.