Bases for bow pulpit
If you have a common boat, you might take this question to a Sailnet email group for your manufacturer - perhpas some company still makes/stocks parts.
If you can''t find a source of OEM parts, see Google.com for sources such as which may have something comparable:
If you can''t find parts you need to see a local SS tubing fabricator about having custom parts made. If you don''t have a volume production boat, my bet is you''ll be facing a rude $urpri$e.