They definitely have material in Eslite bookstore, I seen quite a few 台語 books with audio cds, but you gotta know Mandarin to use those books. I got a book on Cantonese there, it’s pretty good.
When I was in Taipei a while ago I found this cool second hand bookstore next to 士林站
They had a 3 book series for English speakers to learn 閩南話 selling used for 1000 NT each. They also had the audio discs included. I should have bought them, I would bet those books are still there, if someone wants to check it out, they were upstairs on the language shelf. I forget the name of the shop but when you exit the front of the station it’s on the right side just a little bit in the direction of the back of the station.
I tried to find it on google map but it wouldn’t let me go down the lane there but if you are outside of Shi Lin station and you are looking at this 711, just keep following the stores going to the right and it’s down that lane way : ) by the way, that restaurant 3 doors to the right of 711 with the green and white awning is damn good!