You may be able to get a boost control valve s/h from a breaker, part no 7485576, or failing that a main dealer or the upgrade people.
Your ECU will be upgraded on an exchange basis by all of the suppliers below.
There are 3 main companies I would recommend for your ECU upgrade (in alphabetical order)
1.
Abbott Racing
Based near Manningtree, Essex, have been the UK's foremost Saab racing team. Usually a bit more expensive than others but you can take your car down their have have it properly checked over and set up by the experts.
2.
Maptun
Swedish firm, relatively small but know what they're doing. Mail order only needless to say.
3.
Speedparts
Again a Swedish firm, but have a UK outlet through
Elkparts. Well tried and tested within this community.
As for exhausts, there are a number of options.
Abbott sell full stainless steel systems. They are very well made, but quite expensive. The advantage they have over most of the competition though is that they are fully compatible as replacement drop ins for each section of the OEM exhaust.
JT exhausts are available from Elkparts, and again are well tried and tested. Aluminised mild steel construction.
Then there are the likes of Longlife who will manufacture you a custom stainless exhaust while you wait.
HTH