There are several online vendors of hearing assistive technology products. I have no affiliation to any vendor. Some vendors who specialize in HAT have deeper knowledge of these specialized products than standard online stores. This is probably because they are more focused and their customer feedback is from people with hearing loss. Diglo (formerly Harris Communications) has been very supportive of the HLAA N-CHATT program and community. Above all, they offer great customer support through their chat box. You can also find some products on Amazon and other big online stores. Wherever you shop, be sure to check on the return policy. In addition, ask about a possible discount if you are an HLAA member.
Here is a sampling of vendors of hearing assistive technology: