There are actually only three maps you need to get for this and If you know where they are it's fairly simple to get all three. This is easiest to do as a bard, but can be done by anyone. I believe the two you have to buy are 250g each and wont appear if you cant afford them. Also, at no point in this run should you attack rats, always walk away or decline rat related quests, nor should you marry anyone until prompted to in the guide.
In the deep part of the forest jump off the waterfall (50 damage without a barrel item from helping the farmer on the main road.) to get to the elven town. A random encounter in the town allows you to buy the map.
If you are not a bard you will also need to get the musician in this town to teach you how to play music. Theres likely a few ways to get him to do it, but the only way I've done it is with a character with the hero background, but it's highly unlikely that's the only way. Continuing for non-bards you will need to get some gold and then get an event in Alluris to buy an instrument.
To get the next map you will need to get a group of rats to follow you. With music knowledge and an instrument when you encounter rats you should have an option to play music which will make them your followers. Rats spawn in various places, you may just need to wander around for a while and find some.
With rats in tow and having not attacked any during this run, head to the cave on the main road. Somewhere in the cave, I believe in the ruins area, if you have rat followers and haven't killed any, the rat queen should offer to marry you. Accept the offer and the second map comes with her.
Continue to the deepest part of the cave, then take the staircase when it comes up. It has a chance to send you to the Alluris undercity or the dwarf town. For this we want to go to the undercity, so if you end up with the dwarves, head back to the cave and try again. In the under city you should eventually be offered the last map for sale.