I've taken several combination guns to Africa and killed a cape buffalo with a Tikka 512 (same as Valmet 412) in 12/9,3X74R with a second set of 9.3/9.3 barrels. I also used a Simson drilling in 12/12/9.3X74R, a Sauer cape gun in 12/8X57JR, and a Sauer drilling in 12/12/30-06.
All were scoped, the drillings in claw mounts, and the Tikka with a Valmet QD mounts for the two scopes I took for that set.
I don't see much if any use for a light round like the 22 center fires, since small game can be taken with the shotgun. We ate a lot of francolin and Guinea fowl.
A good choice for you for what you're wanting would be a Valmet O/U in 12/22 Svg HP (5.6X52 European name). The 22 Savage Highpower shoots a 70gr bullet, which I think is about right. These can be found in the Lion and 300series guns for $700.00 to $900.00 and take the Sako scope mounts. Genuine Sako 2 piece rings work well as QD mounts. The fine Savage 2400 in 12/222 is the same gun with better wood and a higher price.
These are my Valmets: a Savage 2400 on left 12/308, and a Valmet 330 12/5.6X52R right with second set of 12ga O/U barrels. All barrels fit both receivers.
I recently gave a Valmet 300 series in 12/222 to a good friend, who puts it to good use. He shot this pig with it last season.
Simpson Ltd has a couple that would work well.
http://www.simpsonltd.com/product_i...;osCsid=320a9ee6a8153ae0bc7e1a704bb32e09http://www.simpsonltd.com/product_i...;osCsid=320a9ee6a8153ae0bc7e1a704bb32e09YOU MIGHT get this gun with one of their 22 CF guns, just to have a 12/308 barrel set.
http://www.simpsonltd.com/product_i...;osCsid=320a9ee6a8153ae0bc7e1a704bb32e09