Try EASA in case company manuals fail, in case operating in EU territory.
Try
AMC7 SPA.LVO.100 Low visibility operations - EFFECT ON LANDING MINIMA OF TEMPORARILY FAILED OR DOWNGRADED EQUIPMENT which quotes:
"These instructions are intended for use both pre-flight and in-flight. It is however not expected that the pilot-in-command/commander would consult such instructions after passing 1000 ft above the aerodrome. If failures of ground aids are announced at such a late stage, the approach could be continued at the pilot-in- command/commander’s discretion. If failures are announced before such a late stage in the approach, their effect on the approach should be considered as described in Table 7, and the approach may have to be abandoned.
The following conditions should be applicable to the tables below:
(1) multiple failures of runway/FATO lights other than indicated in Table 7 are not acceptable;
(2) deficiencies of approach and runway/FATO lights are treated separately;
(3) for CAT II and CAT III operations, a combination of deficiencies in runway/FATO lights and RVR assessment equipment are not permitted; and
(4) failures other than ILS and MLS affect RVR only and not DH.
Table 7: Failed or downgraded equipment – affect on landing minima Operations with an LVO approval
...
RVR assessment systems | At least one RVR value to be available on the aerodrome | On runways equipped with two or more RVR assessment units, one may be inoperative
..."
There is guidance that touchdown RVR can be substituted by other readings but this should be in company manuals as Small cog said to ensure it is approved for your company.