Hi Vik
You should be able to bring these groups across into Schoolcomms by changing your import settings to include 'All groups' instead of only 'Active groups'.
There's a bit of a grey area in terms of what is classed as an active group in SIMS but we have found that by changing this setting, schools who have seen a similar issue to yourself are able to import any missing groups.
If this doesn't resolve your issue then please do get in touch with our support team directly.