I may end up having to replace the whole chuck if I can't find the part. Silca brass chucks are around $20 but I have found the Topeak Brass Superchuck for about $11 shipped and it looks like it would do the job.

That said if I can find the replacement part it is likely only a few dollars and the pump has worked well for 30 years and I like the look of the brass chuck.

Thanks.