A new functionality has been added to the Fediseer which should allow people to both find more instances to guarantee easier, and also to help new instances to request such guarantees.
For new instances, you can visit this page: https://gui.fediseer.com/solicitations/create
You can then submit a request to be guaranteed and also optionally provide a comment about it.
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For those already guaranteed, you can now check which other instances are requesting a guarantee in this page: https://gui.fediseer.com/solicitations
You can then further follow up on them, and guarantee them directly from that page.
Likewise requests for guarantees are now also visible in the action log page.
Also, if an instance had a guarantee and it was withdrawn, they will receive an automatic solicitation entry, so that people can immediately notice this and re-apply their guarantee if warranted.
So if you want to help ensure the smooth on-boarding of new instances, do check back on active solicitations and approve them if you think they're legit!