The license held restriction is normally required by the insurance companies the rental places use. If you haven't had your license very long, then you're considered a higher risk due to the lack of experience.
You should find that some places will have a different insurance policy that can be offered, which would let you ride with your license, but likely with both a higher excess and a higher daily rate.
Some big places will have this already worked out as standard, so if you ring them they should be able to quote straight off. Alternately, a smaller rental place ought to be able to ring up their insurers and arrange a one-off for you, possibly for an admin fee (in addition to the higher premiums and excesses....). I'd suggest you ring up a few places and see what they can do.