Namecheap
https://www.namecheap.com/
Hover
https://www.hover.com/
Enom.com
https://cp.enom.com/domainsearch/default.aspx
Name.com
https://www.name.com/domains/build
Porkbun.com
https://porkbun.com/
Network Solutions
https://www.networksolutions.com/
Ionos (iwantmydomain.com)
https://www.ionos.com/
gandi.net
https://www.gandi.net/domain/build/news
TLD Registrar Solutions
https://www.domain.build/
Only Domains (1API)
https://www.onlydomains.com/
Crazy Domains (Dreamscape Networks)
https://www.crazydomains.com/
Wild West Domains
http://www.godaddy.com/tlds/build
Dynadot
https://www.dynadot.com/domain/build.html
EuroDNS
https://www.eurodns.com/international-domain-names/build-domain-registration/
Combell (Hosting Concepts)
https://www.combell.com/en/
101 Domain.com
https://www.101domain.com/build.htm
United Domains
http://www.uniteddomains.com/new-top-level-domain/build-domain-registration/
Cronon AG / Strato / Deutche Telekom
https://www.strato.de/buy/ger/domain/display/3