I think you should be able to use medium sized onaholes, like those that Toysheart, RIDE or Magic Eyes etc make. I own the Love Venus R http://en-nls.com/pict1-20758?c2=36111010
I think Hina and Venus has the same dimensions. I have bought the onahole "Air Pussy (Outhodox)" from NLS which has a plastic tube you can put onaholes into to help with insertion into the doll easier (the onahole itself is quite good also), it works great with my doll so it should work with the Hina. Magic Eyes has made the onahole "Girl's (i)" (NLS) and that seems to be made for love dolls so that maybe is a good onahole to pick up, I have no experience from it though.