Currently Schoolcomms doesn't offer the ability to create a donations page, however it is possible to set up a link to a charity/fundraising page without going through Schoolcomms, you can then add that link in Schoolcomms to enable parents to access the donation page via a link in School Gateway.
How to add a link on School Gateway
Alternatively you could create a payment request via Schoolcomms for the fundraising donations.
Please note, there would still be a 1.27% transaction charge on the full amount taken.