Maya - have you considered Etsy?
I did a quick search and came up with the following:
Polka dots - http://www.etsy.com/listing/40.....B%5D=title
Leaves - http://www.etsy.com/listing/36.....B%5D=title
Stripes (although this is cotton rather than plastic - http://www.etsy.com/listing/28.....B%5D=title
And kind of gothic? - http://www.etsy.com/listing/41.....B%5D=title
Knowing Etsy sellers, I bet that they could make a hat to your head measurements...
I also did a quick google search and came up with this supplier in the UK - http://www.hatsandcaps.co.uk/c.....t-P186301/
If your head is particularly small, you could consider looking in the children's department. My Mum has a really small head and buys sun hats or caps in children's sizes.
BTW - this topic has put the song "Rain drops on Roses" into my head.