This is exactly what you need. Worked perfectly for me.
https://www.ebay.com/itm/266450250815Must be two 4GB sticks of DDR2 PC2-6400U 800MHz AMD (Can't be just PC-6400, must be PC-6400U)
Ships from China. So who knows what stupid tariffs would do. There usually aren't any of these available on ebay shipped in the US available. But there might.
I've also gotten the same memory from some small sellers on Amazon that had a few sticks available. Sometimes a few sticks of them will be listed by a smaller Amazon marketplace seller.
If you do find a source in the US. Just look closely at the chip layout of the memory you're looking at. 2GB sticks only have 8 chips, 4GB sticks have 16 chips.
If it's listed as 4GB DDR2 PC2-6400U 800MHz DIMMs, and it matches the attached pic of the chip layout on the DIMMMs exactly. It's almost certainly the same, a few companies made it, not only Samsung, But it has the exact same chip layout on the DIMMs that will work.