Currently, there is no other GBA emulator capable of the GBA <->GCN functionality. Fwiw, you can keep an eye out of Issue 7098 for future updates.
It's just talk right now, but sometime this year I'm going to begin development on my own GBA emulator. Hopefully I'll be able to work closely with the Dolphin devs and possibly get it working (at least on the GBA's end). That's at least a year out there from now. I'm still working on emulating the GBC atm. Like I said, just talk until I start coding the thing.
EDIT: By the way, version below 4.0 are not supported here on the forums, so if you do want help on getting LoZ:FSA to connect with VBAM and Dolphin (it's basically one of two games that consistently works right now in a playable state, so it's not impossible) you're going to have to use something newer. Have you tried looking at this thread?: https://forums.dolphin-emu.org/Thread-gba-gcn-connection-guide
It's just talk right now, but sometime this year I'm going to begin development on my own GBA emulator. Hopefully I'll be able to work closely with the Dolphin devs and possibly get it working (at least on the GBA's end). That's at least a year out there from now. I'm still working on emulating the GBC atm. Like I said, just talk until I start coding the thing.
EDIT: By the way, version below 4.0 are not supported here on the forums, so if you do want help on getting LoZ:FSA to connect with VBAM and Dolphin (it's basically one of two games that consistently works right now in a playable state, so it's not impossible) you're going to have to use something newer. Have you tried looking at this thread?: https://forums.dolphin-emu.org/Thread-gba-gcn-connection-guide