Wheeler make gunsmiths screwdriver set , you can get different size sets. I have used them for years with no problems.
.22 Venom Mach 1 (FAC) 6-25x56 Millett.
.22 Venom Mach 2 Thumbhole 6.5-20x40 Leupold EFR.
.22 Venom Mach 2 Sporter 4-12x40 Leupold.
.177 Venom Vantage 4-16x50.
.177 Venom Daystate 8-32x56 AGS.
.22 Venom Datstate 4-16x56 AGS.
.22 Webley Venom FX2000 6-18x40 Busnel Legend.
.177 Titan MPT by Steve Pope 6-24x40 Tasco.
.177 Pro-Sport 4-16x50.
.22 Webley FX2000 3-9x33 Leupold EFR.
.177 Logan Solo 4-16x50.
.22 HW90 (spring powered) 4-16x50
.22 Gamo Stutzen.
.177 Walther lever action.
+1 for the bsquare set. I have this and for the price they are excellent. A good variety of hollow ground bits and the extras.
I have a browning auto 5 which has screws with very thin and wide slots - this set works a treat. I think it's about 30 quid
Donald
Brownells sell Bondhus sets which are usually good gear.
You could try looking for "Aircraft quality" tools from general suppliers but they tend to be way pricy as does anything marked for Aircraft use.
I have a Chapman set, American made but I got it from someone in UK (Sorry, cant remember who). Fairly comprehensive set of hollow ground bits, but I still occasionally find a screw I can't match. For guns which I strip regularly I try to fit screws with allen heads wherever possible - saves loads of hassle.