Clockkit has been a constant supplier of clockworks for many years, even pre-web days when I was participating in dialup woodworking bulletin boards, especially for things like grandfather clocks, etc. But for a simply wall clock such as this one, I’ve used battery powered modules from Woodcraft quite a bit.
I’m sure Rockler would also have them, as well as Amazon. I just used a standard quartz movement powered by 1AA battery in this. It is a black box about 2x3 inches and 1/2" thick.
I get clocks from several different places and all of those mentioned above are great!
Goodwill in my area the clocks range from $1.50 - $3.00, take the mechanism and toss the rest.
Hobbylooby I use 90% of the time. Use the 40% off coupon as mentioned, but if you have a smartphone, just download the app and you will always have a coupon, no need to get one off the internet and print it out, if you have your phone on you, you will always have a coupon.
Michael’s in my area have a larger selection and I usually hit them up when I come across a 50% off coupon. (The clock parts are a tad more expensive at Michael’s, but Hobbylobby will only ever offer 40% off, they will never go above that, but it’s okay because you can simply go back the next day and use that same coupon again if you need other parts - but with the 50% off coupon I can get a better deal.)
Joann’s selection is very small, but when they offer the 60% off coupon is when I will get my parts from them.
…and lastly
Ebay super cheap if you don’t mind waiting a bit as they are shipped from China.