Here are some compatible modules via searches at memory manufacturers websites (including 8 GB modules, and also 2 x 4 GB kits) -
Crucial
Kingston
If wanting just 8 GB total memory for the computer, then it is recommended that a 2 x 4 GB dual channel kit be used instead of a single 8 GB module. Two modules in dual channel configuration will provide maximum memory bandwidth; single channel mode with just one module will provide less bandwidth.