I usually get Cisco memory from memoryx.net. You can search by specific devices on there. I've never had issues with any of the memory from them and I've upgraded many different cisco devices, including different models of ASAs, with no issues at all.
Might at least give them a look. They also sell Cisco "branded" memory, which is usually just kingston or hynix ram with a Cisco sticker on it anyway no matter where you get it.