I've been having a hard time finding a solution. Is there really no commercialized model that I can feed in a reference sound and text instruction and get another sound out?

Right now having a multimodal inputs to image or text output is a commodotized, solved problem. IE you can put a prompt for some image and use a reference image to guide the model on what you want. After all, a picture is worth a thousand words right?

Ive also used a text and audio input in order to get a text description or classification out.

I cannot for the life of me find a solution for Audio + text -> Audio

My usecase is that I'm trying to generate new sound effects based on a source that doesn't have that many clean examples and thought this would be just another solved workflow but I'm not finding much. Tried elevenlabs SFX but it's only text->audio and without the reference, it's hard to guide with just text and recreate a sound with any accuracy. I tried the Stable Audio 3 model which is supposed to do what I want but the results were terrible. This modality seems to be stuck where image generation was in 2016. Is there something else or is this just not a common need?

You should look into using AI to generate code that synthesizes sounds. Not exactly what you asked for, but I do think it is an approach worth considering: https://m.youtube.com/watch?v=1-i45X5aj94

Even though they're technically trained for music, it might be worth testing Suno/Lyria to see if they're able to do this. You might have to isolate it afterwards, but seems like it could be viable

https://github.com/OpenMOSS/MOSS-TTS

KeenLore is my locally hosted full-cast emotive audiobook generator I'm developing for my novel:

https://www.youtube.com/watch?v=WAeHgE94rVo

Another HN user suggested embedding sound effects. The lead author of MOSS-TTS emailed me that the next version will have a SOTA voice designer. Poke around the voice design space, you'll find text-to-effects here and there. I certainly have my eyes on this space.

Daydream Music - https://daydream.live

The DEMON realtime engine is open source. The hosted service has a number of integrations with popular audio tools. (I'm on the team)

Maybe a dumb idea, but how good are image models with manipulating spectrogram images? Then a workaround could be: convert input audio to spectrogram -> pass spectrogram + prompt to an image model -> convert modified spectrogram back to audio waveform.

Apparently the AudioX and AudioLDM(2) models do this but I think you've found a genuine gap.

Plenty of models take in text + audio and spits out audio. It's the format of most newer generation accent conversion/voice cloning models.

What's your exact use case?