these two articles are part of a series of boron hydride papers in vol. 75 of JACS. the usual, but with some nice details not found elsewhere on this site, except perhaps in the Post 253798 (missing)
(PolytheneSam: "NaBH4 patents", Chemistry Discourse) patents.
The Preparation of Sodium Borohydride by the High Temperature Reaction of Sodium Hydride with Borate Esters
H.I. Schlesinger, Herbert C. Brown, and A.E. Finholt
J. Am. Chem. Soc. 75, 205-209 (1953)
(https://www.thevespiary.org/rhodium/Rhodium/hive/hiveboard/picproxie_imgs/djvu.gif)
Procedures for the Preparation of Methyl Borate
H.I. Schlesinger, Herbert C. Brown, Darwin L. Mayfield, and James R. Gilbreath
J. Am. Chem. Soc. 75, 213-215 (1953)
(https://www.thevespiary.org/rhodium/Rhodium/hive/hiveboard/picproxie_imgs/djvu.gif)
...and apparatus for producing same. relevant to the above if you don't have anything else to do.
Sodium Dispersions, pp. 6-10
and Sodium Hydride, pp. 10-13
of Inorganic Syntheses Vol. 5.
(https://www.thevespiary.org/rhodium/Rhodium/hive/hiveboard/picproxie_imgs/djvu.gif)