Fatboy,
In D-36, you can request a number in December, and if it is not already assigned to someone else, you can have it. Then you request yearly to retain your existing number.
Numbers 1-150 are assigned to the top 150 riders, but 151-999 are available for request. Then when the season begins, D-36 just starts assigning numbers by lowest available to everyone who does not have one assigned to them.
It may or may not be a similar system with your district. I would check their website if they have one. Hope this helps...