Entre Prises is credited to being the first manufacturer that created and sold climbing holds to the public.
Francois Savigny, an industrial engineer and rock climber, founded Entre-Prises in France in 1983; the US division came to Bend, Oregon in 1988. With manufacturing in the US, France, the United Kingdom, and 28 worldwide distributors, Entre-Prises has completed over 4,000 climbing wall projects globally.
On a different Entre Prises website it mentions: Francois Savigny invented the first climbing hold in 1985 and the first climbing wall in 1990 (Entre Prises).
As far as the question of what company first offered climbing holds to the public which were made in the USA? That answer is a c.1988 toss up between Entre Prises and Metolius and Vertical Concepts.