Are there public LN nodes that have some gRPC LND API endpoints accessible for 3rd parties? My lnd node died but I'm doing some research on lightning channels. So I'm rebuilding a new btc/lnd node, but in the meantime: are there open nodes that I can access, especially for SubscribeChannelGraph?

Update:
I found this repo that pretty much had everything I needed. It's a modular implementation of the BOLT specification in NodeJS, meant exactly for uses cases like mine. 

https://github.com/altangent/lntools
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 listen to the gossip protocol.

However since the transport layer in BOLT 08 is encrypted via the noise protocol framework you will also have to reimplement this in order to be able to connect to a peer. Only your peers can be queried for the network graph from BOLT 07. The only other BOLT that you need is BOLT 01 which describes the message format of peer messages.

Implementing these allows you to interact with the peer to peer network and get information about the channel graph without the necessity to implement a full lightning node or even run a Bitcoin node. In fact you don't even need any of the Bitcoin techstack (just ecdsa for your static node key and strong authentication within BOLT 08)

I might make the network graph available via my lightning node next weekend if I remember to do so. Then there would be an open api command to query for this data. Hope that answer helped.