Any scope mount made to fit No.4s without drilling and tapping or other gunsmithing will fit a No.5 the same way. And if your No.5 hasn't been messed with already, don't have it drilled and tapped. Pay what it takes to get a no gunsmithing mount because you will lose significantly on the value of an unmarred No.5 if you have it drilled.
If you want to be able to use your iron sights and remove the scope easily for access to clean the rifle, try to get a Cad-Technik mount from Brownells in the U.S. It will mount the scope rather high, but you can get a comb-raising kit by Beartooth from Russell Sports in Calgary that will allow you to get a cheek weld when shooting.
If you don't mind taking the rear sight off (and saving it, of course, in case you want to sell the rifle one day) there are no gunsmithing mounts from B-Square, S&K and ATI in the U.S. that can probably be ordered from U.S. and/or Canadian retailers, and from Armalon in the U.K., who I think would have no trouble shipping here. The one FirstBMW refers to from Marstar looks to me like an Armalon copy or perhaps they get it from Armalon. I think these are all cheaper than the Cad-Technik mount.
And if you search this site you will find we have done this topic several times, so there is more detail available if you find the old threads.