If you rejected a query or manuscript, but that manuscript then went on to be published in a foreign market (ie the UK) to substantial success and the author wanted to find a US agent to sell the rights for the North American market, would you be prepared to look at the manuscript/query again?
If you want to discover the truly bizarre things agents fight about with publishers, all you have to do is say "Open Market: India"
People in the UK speak English. I know this isn't a shock to you of course.
People here in the US speak it also.
Thus, if you sell a book in the UK it's not quite the same "foreign market" that say Urdu or Sanskrit or Klingon is.
In other words, you'll need to have retained North American English rights AND open market rights for a list of countries outside the British Commonwealth..
UK publishers do not put India on the open market list.
US publishers do.
Trust me when I tell you it's an ugly fight.
We also like to brawl over Malaysia.
There are other points of contention as well.
Your UK contract was most likely drawn up to favor the UK publisher. Without looking at it, I can't tell you if it's got enough territory left over to interest a US publisher.
If you sold into the UK market without an agent to help you on this arcane but important point, chances are you granted world English to the UK publisher. That means you CAN'T approach a US agent for sales here; those rights are held by the UK publisher.
I will tell you that lots of books do find an American audience after some success in the UK.