As far as I know, there are no open nodes anywhere. But I did not look for them. Generally, you do not need a complete node / full implementation to extract data from the lnd subscribechannelnel command.
Basically, you just need to reimplement BOLT 07 (https://github.com/lightningnetwork/lightning-rfc/blob/master/07-routing-gossip.md) to listen to the gossip protocol.
However, since the transport layer in BOLT 08 is encrypted via the noise protocol structure, you will also need to reimplement it. In addition, you will need to connect to a peer by implementing the BOLT 02 protocol. Only your peers can be queried for the network graph from BOLT 07. The only other BOLT you need is BOLT 01, which describes the format. message counter messages.
Their implementation allows you to interact with the peer-to-peer network and obtain channel graph information without having to implement a full Lightning node or even run a Bitcoin node. In fact, you do not even need Bitcoin technology (only ecdsa for your static node key and strong authentication in BOLT 08)
I could make the network graph available via my Lightning node next weekend if I remember doing it. Then there would be an open API command to search for this data. I hope this answer helped.