Of course Sienci Labs sells bits on their site. They are a good price but if you cannot wait for shipping or need it right away here are a few sources you can get them from.
https://www.leevalley.com/en-ca/search?query=1%2F4+shank+router+bits Search for other types
https://bitsbits.com/ May be US only shipping Not sure
https://www.busybeetools.com/categories/Cutting-Tools/End-Mills/ Search for other types
https://www.normand.ca/en/normand/cutting-tools/router-bits.html search for what you need they have a basic kit available.
https://www.atlas-machinery.com/searchresults/search-results/?search_query=end+mills Search for bit styles you may want
Please feel free to add other sources below. Add the website please and to keep the thread clear please do not post other items in this thread. I want it to be a tooling resource. Thanks guys. Oh please add the country the place is in for clarity. All the above are in Canada except Bits and Bits.