I recently purchased a 19" Satori riser. It's mainly for my son but it can also serve as a back up bow for me.

My draw length is 27" AMO. What's the best length of limb to suit this?

My DL is 27.5.  I also have a 19" Satori riser.  For me, medium ILF limbs which result in a 62" bow are ideal. 

I also have a Bob Lee Ultimate, also a 19" riser, non ILF but with their Stabi-lock limb mounting system, with Bob Lee limbs making a 60" bow. The performance of the 60" bow is probably a little better at my DL, because the shorter overall length gives the recurves a little better workout.  This would be the equivalent of short ILF limbs.

But overall, I seem to shoot 62" bows better than 60" bows, so I'll probably stick with that length in the future.

BTW, if you're looking for limbs, 3 Rivers has Uukha limbs marked down significantly to make room for the new models.  Uukha Selenga are fabulous limbs in my opinion, especially at the reduced prices.  Don't know how much good this would do you in Australia, but maybe they're marked down wherever you buy limbs too.

I checked out the 3Rivers site for the uukha limbs. They don't have anything in the 55# weight I want.

I would look at either shorts or medium.     I personally like the 3 rivers das 3k carbon bamboo limbs.   But there is nothing wrong with uukha, win win , Bosen or nika.   

A 19" riser with your draw length I would go with shorts. You will capitalize on the limbs performance going with shorts.

I consider the Samick R3 limbs a great value, they are carbon/foam, quick, stable and very quiet limbs. I use Long limbs on a 19" riser and it makes for a great setup.

I too would go with shorts.  A bit harder to find shorts vs mediums or longs.  Not hurting anything with mediums but the extra performance would be my reason.  I like a snappy limb where the tips are working more at your full draw.

I recently bought some used uukha limbs for my son and I'm impressed.

I've been looking for some in 55# but can't find anyone who seems to have stock of anything in the weight.
Anyone know where I might find something?

RMS Gear lists 55# Uukha Uureg limbs for $895 (not on sale).  These are 100% carbon, and are supposed to be a step above the Selengas.  I also have the Altai's, also 100% carbon, and love them, but they have a propensity to break.  I haven't heard that the Uuregs have that problem.  From all reports I've read, Uukha has been willing to replace any Altai that breaks, in or out of warranty, but I don't know how much comfort that would be for you in Australia.  I've bought things from RMS Gear, including some things I have returned, and have been very impressed with their customer service.