Reddit mentions of Sunlite Cruiser/MX Steel Brake Set, 73-91mm Reach, Chrome

Amazon or eBay will have a brake kit.

CNC Adaptor: https://www.amazon.com/UAUS-Sprocket-Adapter-Motorized-Bicycle/dp/B07ZJ3STLC/ref=sr_1_6?crid=1RF5YNX546933&keywords=motorized+bicycle+sprocket+adapter+kit&qid=1574881286&sprefix=motorized+bicyle+sp%2Caps%2C319&sr=8-6

Disc Brake kit: https://www.amazon.com/BlueSunshine-Front-Back-Disk-Brake/dp/B07458MXNB/ref=sr_1_1?dchild=1&keywords=motorized+bicycle+disc+brake+kit&qid=1574883409&sr=8-1
Note: The CNC hub has a 6 bolt pattern near the center of the hub to bolt the rear disc onto. If you wish to use disc up front, you will need a front wheel or hub that can adapt to disc brakes. You can also find 26" wheels with these disc brake hubs already installed.

Front disc brake will need one of these: https://www.amazon.com/Fashion-Life-Adjustable-Bracket-Mounting/dp/B019OML8VE/ref=pd_bxgy_468_2/136-3711700-3661816?_encoding=UTF8&pd_rd_i=B019OML8VE&pd_rd_r=9be28cda-a6eb-4e2e-917e-90974ef50b31&pd_rd_w=wq72u&pd_rd_wg=XttIU&pf_rd_p=09627863-9889-4290-b90a-5e9f86682449&pf_rd_r=26T3QTM8CF54HNDW67HP&psc=1&refRID=26T3QTM8CF54HNDW67HP

For the front, you will need a new front wheel. https://www.amazon.com/Alex-Rims-Alloy-Front-Wheel/dp/B01FWHAHEE/ref=sr_1_1?dchild=1&keywords=26+x+1.75+bike+rim+disc&qid=1574887171&s=sporting-goods&sr=1-1

Disc Brakes are ideal, (better stopping) but if you don't want to go the hassle of installing them, you can instead opt for v brakes.
https://www.amazon.com/Sunlite-Cruiser-Steel-73-91mm-Chrome/dp/B000AO5J16/ref=sr_1_12?dchild=1&keywords=motorized+bicycle+v+brake+kit&qid=1574883735&sr=8-12

Use this video as a guide to installing disc brakes on your bike (please note, the rear disc will be bolted to the motorized bike sprocket, so, its mainly good for the front.
https://www.youtube.com/watch?v=emW7M-ZD0Pw&t=104s


Also, if you prefer "Mag" wheels as opposed to spokes, here's a nice set of BBR tuning mags for $119. These Include the motorized bicycle rear sprocket, so the above listed CNC Sprocket Adapter will NOT be needed if you buy these wheels. The Mags are disc brake ready, no additional adapters needed outside of the front and rear caliper mounts.

https://www.amazon.com/BBR-Tuning-Mountain-Cruisers-Motorized/dp/B076PWYSFS/ref=sr_1_10?dchild=1&keywords=bicycle+disc+brake+wheel&qid=1574884536&refinements=p_n_feature_six_browse-bin%3A6404041011%2Cp_36%3A-20000&rnid=386589011&s=outdoor-recreation&sr=1-10

Make sure everything fits your bike before purchase. Also, feel free to do some research.