Had a very frustrating afternoon and evening yesterday looking for this fare without success - not really for the do, I think it'd be difficult to be social during something this intense, but because trying it is almost irresistible.
I was able to find £550 returns to PTY no trouble, and I could find "I" availability on all the legs I needed individually, but if I put them together I got "no fare found" on the YVR to LAX part. Looking at the fare rules, I think I was maxing out the transfers or something like that. I think @
nufnuf77 mentions this above, the rules have maybe changed. So eventually I gave up. Learned a lot though.