good luck - you'll need it, sorry!
The major "good" companies are unlikely to rent to you, while the smaller hungrier ones might. However remember if you have an accident, you'll be seriously liable, as the authorities take a dim view of riding without a license.
My recommendation: Rent a DIRT bike and go trail riding for practice. When you're easily comfortable with the bike take a ROAD BIKE lesson series for the road part for your OWN safety, and then take the test. Riding a bike on the road is a lot more complicated than driving a car - there's MUCH more to pay attention to and it's all MUCH more critical. Unless you like hospitals...
Take care and do it right please - we want to hear more about your adventures in future years!
Seek, and ye shall find.
Inspiring, Informing and Connecting travellers since 1997!