Here's a jq command to get all the channels with discounts

lncli describegraph | jq -r '.edges[] | (select((.node2_policy.custom_records."55555" != null) and (.node2_policy.custom_records."55555" != "0000000000000000") or (.node1_policy.custom_records."55555" != null) and (.node1_policy.custom_records."55555" != "0000000000000000"))) | .channel_id'

Currently showing 5 (of 16 nodes on 0.18) with discounts