Why hydrofluoric acid (HF) has two Raman bands?
I've been doing some digging and I think I have a possible answer so I'm gonna post it and if I'm misinterpreting information, I'm open to being told so!

As I said in my comment, this vibration has to be coming from some dimer which is formed because if one of these modes were the $\ce{HF}$ fundamental it would be up around $4000\ cm^{-1}$.

So, I found this paper which uses FTIR to analyze $\ce{H2O/HF}$ complexes. They find two librational modes (which I believe is just a solvated rotational/rocking mode basically) which they identify as coming from the $\ce{H2O--HF}$ dimer. They assign these two frequencies at $635.5\ cm^{-1}$ and $753.1\ cm^{-1}$. Those two values are extremely similar to the frequencies we're seeing in the spectra you posted which is why I think we might be on to something here. Unfortunately I don't have access to the paper so I can't go into any more detail really.

In answer to your question of how we could even be seeing multiple peaks in an $\ce{HF}$ spectrum, the answer is that we're not looking at just $\ce{HF}$ here!

We know that both $\ce{H2O}$ and $\ce{HF}$ are very strong hydrogen bonding molecules, so it's no surprise that we find peaks which are associated with the various vibrational modes of the dimers present. And, once we have a dimer, we expect to find all sorts of rotational and vibrational modes.

So, to conclude, I'm fairly certain that the modes we're seeing in this spectra are two (and I think the only two because my digging around says this dimer has $C_s$ symmetry) librational modes of the $\ce{H2O--HF}$ dimer, each rotating about a different axis of the water.



Source:

Andrews, L., &amp; Johnson, G. L. (1983). FTIR spectra of water–hydrogen fluoride complexes in solid argon. Evidence for inversion doubling in the HF librational modes of H2O––HF. The Journal of chemical physics, 79(8), 3670-3677.