With the BLM record number, I suggest you contact the textual reference staff - email@example.com Most likely this record has not yet been digitized and added to the Catalog. The reference staff would best be able to help you.
If you want to search the Catalog using and advanced search and knowing the record group, I suggest the following steps:
1. Click on Advanced Search
2. Place the Record Group Number in the Record Group search field. Then add the BLM record number in quotations in the search term field and click Search.
3. If you do have a list of results, use the filters on the left to refine your search to the correct time period, etc.
Community Manager, National Archives Catalog