You could try a Content Manager search with filters set to Installed = True and Category = Track Object.
This will bring up the "working versions" of various buffers, bumpers etc, along with thousands of signals and other trackside items. Adding a name filter with "buffer" or "bumper" will isolate those. I've never heard of stopblocks, but you could try that in the name filter too.
With filters set to On Download Station = True and Category = Track Object, you will find active bumpers/buffers available on the Download Station.
There are often "non-working" scenery versions of the same buffers/bumpers if you need them. Once you've found the active versions, you could search amongst their authors' creations and see if you can find them.
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