I live in California, and am finding surprisingly limited sources for these. fbrc8 has them for $18 + $6 shipping, which seems a bit pricey for this one part. The only other alternative I've found is getting one shipped in from Europe or China. The price from China is more what I expected:
https://www.aliexpress.com/item/2Pcs-3D-printer-accessory-Ultimaker-Hot-End-Isolator-Coupler-PTFE-Teflon-inner-sleeve-for-3mm-filament/32323348288.html?spm=a2g0s.9042311.0.0.125f4c4diYj8d2
but is going to take 2 to 3 weeks. Will let you know if it's any good.
If anybody knows a good source for these, please let me know. I presume the UM2 one wouldn't work in a UMO+?