I think switching to a different broker will not solve your problems.
Tender offers made outside the US are very often explicitly not made to residents of the US because small companies can't afford to comply with US regulations (Canada, Japan, Australia are other countries I often see explicitly excluded). I took a look at this tender offer, and while it doesn't explicitly exclude US residents it states that it is made only in France, from google translate:
Odds that any broker is willing to submit your shares and that the company is willing to purchase your shares: 0.0001% (okay, that might be a bit too pessimistic)
Besides that, writser is making some good points.