These bandoliers would work great for your small mags. Generally they come filled with ammo on stripper clips in cardboard boxes, but can be bought empty for cheap.
When the cardboard boxes are in them and filled with ammo, the pockets are lightly sewn smaller, after loading your spare mags, see the white thread that’s sewn across the pockets, it is a quick release pull. Grab the end of that white thread and give it a tug, it zips itself right out of the bandolier opening up the pockets to perfectly fit 30rd mags. Leave it intact, and it would probably fit your 10’s perfectly for your purpose.
When the cardboard boxes are in them and filled with ammo, the pockets are lightly sewn smaller, after loading your spare mags, see the white thread that’s sewn across the pockets, it is a quick release pull. Grab the end of that white thread and give it a tug, it zips itself right out of the bandolier opening up the pockets to perfectly fit 30rd mags. Leave it intact, and it would probably fit your 10’s perfectly for your purpose.