Use Go Fund Me! That's what I use.
I would ask around like the handmade tack /etsy. but as long as you ride on a regular basis and you have free access and the owner is ok with u trying out new things u should be fine
Brands like people who are well known either on social media, in several big show circuits, or in both.
Brands usually want someone with their own horse
Maybe ask people who may be willing to sponsor?