If the "searches" are keyword searches then a
good web programmer could put this together quickly.
What you are talking about is what database developers often
refer to as a "database mediator:"

A high level query is sent to the mediator.
The mediator re-sends the query to N-different databases
and then collects N-different results in a a single,
concatenated answer, which is returned to the original
posting form.

When the query is a complex statement, that has to be
translated into N-different dialects of SQL, and then sent
off to a N-different relational databases, in that case
building the mediator is a major undertaking.

But if the query is just a list of comma-delimited keywords,
then there is no query translation step to go through.
A journeyman web programmer should be able to put a
form system like that together in an hour or two.