Good luck finding a pair of rear shocks for an Omega Elite.
If you find a source ,please let me know where from, and how much. 
My VX dealer states they can do the work, and have quoted £237.60, all in, to do it. I will be accepting that next week as I cant be bothered now , too aged, to do that type of work, let alone finding the right shocks!
With them looking after my old beast as they have on and off for years, with them always treating her with great respect- they do not have another Omega on their books - and me knowing their General Manager, Service Manager and Parts Manager for a long time, why not! My MOT cost just £35 because of these contacts.


To reinforce what TB has said.
The price you have been quoted is probably a similar amount they would have to pay for each self levelling damper - if they could actually be found.
So they will not be fitting like for like but using standard (2.6 spec) dampers.
This is fine. I have done the same when one of my S/L dampers burst its bladder.
Thing is, the rear springs
must also be changed at the same time. S/L spec spings are far too soft to work in conjunction with non S/L dampers.
To leave the original springs on the car will imo leave the car in a potentially dangerous condition.
You may not notice just driving around town, and may well not have a press on driving style these days, but in an emergency situation the handling will be a lot worse, and unpredictable, which is dangerous.
Doc Gollum can provide a link for Kilen springs, which arent that expensive, and will do the job nicely