At this stage it depends on the model Bing you are running.
A type 2 Bing 54 (eg 54/38/106 stamping etc, ~42mm dia slide, slide stamp # 220 or 230 etc), Andre at Enduro Klassiker can sort you out.
If its the earlier type 1 (eg 2/36/102 stamping etc , ~40mm dia slide, slide stamp #1 or #2 etc), i am waiting on a reply from Andre for availability of parts through him for these. Else you can try Al Beuhner at pentonpartsusa.com
I am about to rebuild a type 1 for a guy, hence seeing if available from andre as i am after type 2 parts as well for myself.