You have to get coordinated. Hopefully they will see this as a way to avoid over-lap and not an attempt by you to take any leads.
Offer to put together a list for them. Maybe you could offer to pay for some type of qualified list. Ask them to provide a list of their existing customers and prospects. Create a full list marking yours and their's. As a benefit to them, you could provide additional leads. Again, they won't go for this if they feel you are trying to take advantage.
If you are trying to rely more on resellers instead of your own direct sales. This could be a start to manage your reseller network as you grow and possibly create some territories. Providing qualified leads could be a way for you to 'follow-up' on resellers to motivate them to sell your product.