Firstly let me apologise for the spelling in my last post - I have a problem with my laptop - it may be dying - if I type at any speed at all it drops characters all over the place!
If my reading of the site is correct then since the wedding took place more than 75 year ago you should be able to use the scotlandspeople website to get an image of your required certifcate for £6. Register, buy your 30 units, use 1 on the search for the certificate and then another 5 or so (from memory) on obtaining the viewable copy which you can the print off. With any luck you'll still have another 20 odd units left to do some more searching!! You do need a suitable viewer program on your computer but I think it prompts you to download this if you haven't already got one. It's so long since I first used the site, I can't remember, but I know I didn't have to pay for it.