NA take a look on the Bucas Ireland website - in particular their discounted factory outlet. the prices are only available to residents within Ireland - I have got some fabulous pony sized bargains for the donkeys from there. Not entirely sure how their sizing compares to horseware though but I believe you can send them back if they don't fit
https://www.premierequine.co.uk/pony-titan-100g-lightweight-turnout-rug-c2x21442960 any good? I find the bigger sizes maybe come up a little bit bigger than Amigos if that's any help.
I buy the weatherbeeter 1200d rugs (their cheaper ones are 600d so watch for that) for Jess, I really like them and they last brilliantly. For the ponies my favorite is ruggles, Hanks is super cute but fits him better than others as they actually cut their small and giant ones different to 'normal' horse sizes so they fit really nicely around the neck/shoulders, and they are 1200d.