I have for sale a side by side saddle plate that can be used to mount a main scope and a guide scope side by side.
It's made by
Geoptik in Italy. I used it on an EQ6 but it should fit a range of mounts with the Vixen style dovetail.
Price $160
Specs (in Italian)
Staffa in alluminio anodizzata per supporto 2 telescopi.
Lunghezza : 320 mm
Larghezza : 100 mm
Spessore : 20 mm
Interasse : 215 mm
Peso : 1 Kg
I have not confirmed these measurements, but they sound about right to me. (i.e. 320 x 100 mm)
James