It's not exactly petite, but you could try looking around for Brazilian cut swimsuits. Those are cut much smaller than American suits, so on us petites they actually fit very well. Rio de Sol makes REALLY cute suits and they list
http://www.brazilianbikinishop.com/en/ as one of their online retailers. Their bikinis run from about 40 Canadian dollars and up for the top and bottom as a set. And I can vouch for Brazilian lycra, it's much thicker and nicer than anything we get in the States. Their XS bikinis are right around your measurements. I hope this helps!