Is your iSHELL mode not listed here?
Or is the blaze spectrum more than a year older or younger
than your science spectrum?
You can proceed without blaze shape correction, but it will
give you curved order shapes. This could be OK
for some science cases (e.g., when analyzing isolated emission
or absorption lines).
If not, ask the IRTF staff (aboogert@hawaii.edu) to create a blaze
spectrum.