For all ZerOS consoles (excluding FROG2), we support GDTF files which can be downloaded straight from the fixture manufacture (or the GDTF Share site). If the fixture manufacture refuse to make a GDTF file available, first complain to them, but then use the various tools available - filtering & fixture creation directly in ZerOS, or the fixture builder on the GDTF site (or, last resort, the legacy Zero 88 fixture editor). If there's RDM, a basic fixture personality will automatically be created if there isn't on in the library.
For non-ZerOS consoles, if the fixture isn't already available, the Zero 88 fixture editor is available to easily and quickly create fixture files (remember most of these consoles, such as Jesters, do not use any of the details / images / colours etc. So they just need channel name & order, appropriate attribute, and the default value).
The above are, by far, the quickest options. Alternatively, email the Vari-Lite support team at entertainment.service@signify.com