Dougy,
You are doing exceptional things, no doubt. Trouble is, exceptional effort is required due to the lack of a salable item. To me it's a no brainer that a sport which has 7 days per week, day and night presence and has such a wide ranging competitor base SHOULD be so easy to sell to a sponsor....BUT it is not. That there is the evidence that a flaw exists. (there is plenty more evidence if you care to stand back and look with an open mind about our sport.)
Signage has lost it's effect to a large degree and is rarely even taken notice of, the reason sports are being sponsored by the biggest businesses across the world is the emotional factor of association with the fan's favourite team that gives the value to the sponsor. I'm sorry to say, your efforts will not likely build a base which will increase as time goes on. You will struggle to retain sponsors because they simply will not be able to see a return for the dollars they invested. It's not your efforts that have the problem, its what you are selling