Testing an upload of my catalogue island, clothes island 1, clothes island 2, and materials island. I believe it has everything that was catalogueable in 1.2, not sure how much difference there is from 1.3.1, probably just some swimming clothes. Test it out, see if it works
For best results, import acres first, then import terrain, then import buildings, making sure to change Plaza X to 106 and Plaza Y to 150, then import Items last
edit 1 - in the materials island, there are all the new 1.3 items on the beach in south west
edit 2 071320 - updated clothes island 2 to include all DIYs up to and including the mermaid DIYs
catalogue island, includes all items in all variants, all rugs, all flooring, all wallpaper, all KK songs, all villager posters
clothes island 1, includes all tops, bottoms, dresses, and some hats
clothes island 2, includes the rest of the hats, accessories, socks, shoes, bags, umbrellas, all DIY up to and including mermaid DIYs
materials island, includes 40 stacks of each material, except for a few which only has 20 stacks of each material (ie zodiac shards, can always just reload the island in JKSV and pick them up again if need more), and all the new items from 1.3.1 in lower left (wetsuits, mermaid stuff, pirate stuff)