One of the biggest challenges for new or growing brands when approaching multi brands (whether on or offline) is convincing the retailer of the following:
a) You can delivery the product as promised
b) It will sell and do so at an acceptable margin
c) That you can find a way to cover them if b) fails

If you are approaching them as an unknown and are getting significant push back, then your best bet is to ensure that they feel comfortable with the inventory risk they're taking. Here are 3 different ways in which that can be done:
a) guarantee their margin
b) sell on consignment
c) offer a return guarantee ("put it on wheels")

I generally only recommend c), as guaranteeing retail margin can become a drain on your own margin, while selling on consignment means you have to wait to get paid until the product is sold by the retailer. I therefore suggest to offer an upfront return agreement (either x%, or if you want to get really aggressive, take back anything that doesn't sell). The point is to cap their risk and make them feel comfortable about taking a shot with a new and unproven vendor. Make it clear upfront that this is for the starting season only to test the brand, so that they don't expect to maintain that kind of return agreement forever.