I'm looking for a lora named <lora:colorify:0.3>, searched in the usual places (hugginface, google keyword search, /sdg/, r/stablediffusion) but cannot find it
I'm guessing you have seen it in some prompt. If you can not find it, it is quite possible it is simply a private LoRA of the image creator, never shared and perhaps not even meant to share. But you can always try to contact them and ask more about it - if it's not private, they might have a copy to share or at least point you to the right direction.
I'm not sure, but the name seems vaguely familiar. It might be one of the various loras' filenames, since these aren't searched like model names, but I definitely don't have one with that exact name (perhaps getting confused with colorize https://civitai.com/models/153676).
Anyway, as doli says, your best bet is the prompt creator. Personally I wouldn't go to extreme lengths with the search though, there are quite a few decent loras for such a task already.