Bob,
As the OKI is an LED printer it runs hotter than a normal laser printer and so normal vinyl will more than likely melt in the machine. You will need a polyester material to print on which is much more able to withstand the heat generated by the printer. This is available in matt and gloss white and clear from The Magic Touch, LG Signs and Dorotape to name three. There is a small issue with the OKI in that (particularly with gloss polyester), there is a slight greying of any white areas on the sign as it passes through the printer, although in reality this is hardly noticeable.
Expect to pay around £70.00 per hundred A4 sheets.
Hope this is of some use.
John 🙂