Mate there is nothing special at all about ULN2081 or 3081. They are just an array of seperate, general purpose transistors put in an IC package simply for assembly convenience.
You could very easily make up a replacement with seperate BC547's - I certainly wouldn't be paying anyone big bucks for them....
Agree and one way to do this fairly neatly and reversibly without bodging the original board is to install a socket in the original board location. Then make up your substitute circuit on veroboard or similar and wire this with flying leads to another socket that can plug in to the original location. So the original board is preserved and if you ever find the original component at a fair price you can just plug it in.
