Where do you buy maternity clothes over a size 18?

My sister is about a size 22, we went shopping for maternity clothes but there was nothing over a size 18. She has grown out of her normal clothes and needs something other than trackies to wear. She ended up getting some size 26 tops from Kmart but she will probably grow out of them towards hte end of her pregnancy.

Surely there are funky maternity clothes out there for bigger girls? Does anyone know where?