Where can I get an SSD

Since you have an MCP89 machine (320M), the PCH is nForce based. These do not support SATA III* like the 2011/12 HD Graphics systems. As such, you either need an autosense SSD or a SATA II/III compatible model to upgrade this Mac. Because of the limited PCH, you pretty much can only use Samsung drives unless you get a DRAM-less drive with legacy compatibility like the PNY CS900. I do not know of any DRAM SSDs with legacy support other then Samsung. Similar advice with the SSD as the RAM - get 1600MHz RAM so it can carry over to the 2012’s (with a new HD cable done early on so you know it’s done). I am no longer recommending 2011’s if you can swing the extra cost to have Metal 2. The SSD iFixit sells is NOT SATA II friendly.

*With a new HD cable. Original cables cannot be trusted. I would still recommend installing the 2012 HD cable and patching it even in a 2010 as an insurance policy.

See this post: Will Crucial MX500 2TB 3D CT2000MX500SSD1 SSD work in my Mid-2012 MBP? for patching information and get this HD cable (2012).

As far as the RAM goes, it can be taken up to 8GB max OR 16GB if you have the latest EFI firmware and 10.7+ installed, so there are some conditions- again, MCP89 issue that was resolved with the Intel PCH in 2011/12 which can take 16GB from day one. If you want to do it, the cost to do so isn’t outrageous and is worth it - just make sure you get forward compatible ones like 1600MHz so if something happens and you want an upgrade, you can carry the RAM with you.