Unverified. Insert the GBA cartridges to find the following Pokemon (you still need to find and capture them yourself).

Ruby
Seedot -- Hakutai Forest, Route 203, Route 204
Nuzleaf -- Route 229
Mawile -- Iron Island
Zangoose -- Route 208
Solrock -- Thrust Lake, Thrust Lake Surroundings, Wisdom Lake, Aspiration Lake, Tengan Mountain, Departure Springs, Return Cave

Sapphire
Lotad -- Route 203, 204, 205 North, 212 South
Lombre -- Route 212 South, 229
Sableye -- Iron Island
Seviper -- Route 208
Lunatone -- Thrust Lake, Thrust Lake Surroundings, Wisdom Lake, Aspiration Lake, Tengan Mountain, Departure Springs, Return Cave

Emerald
Pineco -- Hakutai Forest, Route 203, 204, 229
Gligar -- Hard Mountain, Route 206, 207, 214, 215, 227
Shuckle -- Route 224
Teddiursa -- Route 211, Wisdom Lake
Ursaring -- Wisdom Lake, Route 216, 217

FireRed
Caterpie -- Route 204 South
Metapod -- Hakutai Forest
Ekans -- Route 212 South
Arbok -- Safari Zone
Growlithe -- Route 201, 202
Elekid -- Route 204 South, Powerplant

LeafGreen
Weedle -- Route 204 South
Kakuna -- Hakutai Forest
Sandshrew -- Lost Cave
Sandslash -- Route 228
Vulpix -- Route 209
Magby -- Hard Mountain, Route 227

Any Pokemon GBA Cartridge
Haunter -- Forest Mansion
Gengar -- Forest Mansion Room with eyes