Is that the lens itself or the entire head width? Nitecore makes something that looks like it fits over the entire head that might work. Check this out
Yes, the Nitecore red filter would be perfect if it would fit.
20mm is entire head width.
23mm is too big, but if I can’t find something else maybe I will try that one and try to pad the extra space somehow.
I asked Battery Junction and they said they don’t have anything that size (which was surprising, given how many different ones they have, but they were all listed by make/model instead of size, not sure how hard they checked on it).