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As far as I know there are no open nodes anywhere. But I have not been searching for them. Generally you don't need a full node / a full implementation to get the data from the lnd command subscribechannelgraph.
Basically you will only need to reimplement BOLT 07 ( https://github.com/lightningnetwork/lightning-rfc/blob/master/07-routing-gossip.md ) to ...
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