Tool to Search United.com Availability & Book on United.com other than Google Flights
 

I am trying to book one of the recent deals discussed. I have flight credit on UAL so need to book through United.com.
I can find lots of great options on ITA Matrix and Skyscanner, but sometimes UAL is not one of the places referred to. Google Flights has pricing, but not all of the routings / connections options (much more limited). United.com has nothing - you can plug in the flights manually and somehow the $1900 ticket becomes $9000.
Is there a way to force ITA or Skyscanner to direct to United.com? Or is there another tool?
Thank you everyone for wonderful ideas, leads, and suggestions. All very invaluable!
Apologies in advance if this is the wrong place to ask this. I have done a lot of searching on this and just can't find anything to address the problem of needing to book with UAL due to credit.

I don't think it's the right subforum.

Have you tried ITA Power Tool?

Might be better to ask directly in the thread of the deal you're trying to book. Some deals are inherently not available directly through the airlines, and can only be booked via OTAs. So, it might not be a matter of tools.

Also some flights are cheaper as codeshares so the desired price is inherently unbookable from the operating airline.

https://bookwithmatrix.com/

This may be of some use.

This doesn't deep link to United.com as far as I'm aware.

Are you starting from the credit and making a flight change (bad) or starting from scratch and trying to book the flight (good)? There have been numerous reports of incorrect prices being calculated when you start from an unused flight coupon and treat it like a change.

Do the flights you're looking for have UA flight numbers? When you construct them on UA, are the flight numbers exactly the same, or has one become a codeshare / stopped being a codeshare / etc.?

Thank you all for very helpful input.
Google Flights seems unique in its ability to deliver an itinerary to United.com for purchase. Are there any other search engines that do that?
As noted, BookWithMatrix does not do that unfortunately (it is great otherwise).
In response to question on other items, it is not those other issues on codes, etc. After an hour online with a very good UA agent feeding them codes from ITAMatrix, UA was able to construct it, but understandably not ideal. Woudl be great if other options in addition to GF. Or maybe there are tweeks to get GF to do more? Or a way to get FlightScanner to do it?

I'm not aware of any others. Google appears to have secured a way to access a United API* directly to create itineraries. I suspect Google drives enough traffic that UA was willing to work with them. Most other sites don't, and UA doesn't have any public APIs for this kind of thing.

I'm curious as to what the route was, now that you've booked it successfully. I've had reasonably good success using multi-city search on Google Flights, picking out each connection city individually. It's not 100%, however, and AFAIK there's no way to guarantee a United booking link.

* Application Program Interface -- think, a specification for how computer systems should communicate.

I called UA Web Support and found an incredibly helpful and patient agent who was able to work with an existing reservation to find the exact routes I wanted on the exact dates I wanted even including a hoped for 1 night layover in the return connection city. AND, she was able to knock $500 off the prior found similar flight. Prior agents had only found routings that increased the fare.
So it was
BUD to FRA to SFO
SFO to FRA / 1 night requested < 24 hour layover / FRA to BUD.
Approx $2000. All in Business. Booked using existing multiple UAL credits.
Wonderful!
Above was even better than what was on GF, ITA, or Skyscanner. And if booked on UAL.com it was $12k.