Niagen/Nicotinamide Riboside (NR) sources?

[MWLE]

I am in the US. I am looking at a good NR/Niagen product for my dad. I have seen people using TRU NIAGEN. Are their other brands that are good and where do I source it? I primary use Amazon have no issues order from some other sites.

I like some that is easy to swallow but strong enough so he doesn't have to take too many.

Thank you!