Apologies if this has been answered previously (I did a search and could not find the answer). I'd like to use UA miles to upgrade from PE to J on TG. According, to KVS, the correct upgrade booking class on TG to do this is "I". Does anyone know the best method to search for I class on TG? As far as I can tell, neither EF nor KVS provide this inventory using any of their search methods.

Also, in people's experience, are these kinds of upgrades relatively easy to get on the LAX-BKK sector, or are they virtually non-existent unless booked a year in advance?