ShowBoardsMUI is not a seperate archive on Aminet, it is part of the library archive itself, along with some CLI tools.
Just skimmed the .guide file for the archive and noticed a note in there saying ShowBoardsMUI has been removed.
Contents of util/libs/BoardsLib.lha
PERMISSION UID GID PACKED SIZE RATIO METHOD CRC STAMP NAME
---------- ----------- ------- ------- ------ ---------- ------------ ----------
[unknown] 11971 31444 38.1% -lh5- 9465 Jul 26 19:05 BoardsLib/Boards.guide
[unknown] 214 464 46.1% -lh5- 0039 Jul 26 19:04 BoardsLib/Boards.guide.info
[unknown] 2235 4698 47.6% -lh5- 9564 Jul 26 18:46 BoardsLib/BoardsLib.readme
[unknown] 3453 5952 58.0% -lh5- ecb1 Jul 26 18:58 BoardsLib/c/showboards
[unknown] 5817 9124 63.8% -lh5- 9c8c Jun 16 21:33 BoardsLib/c/showboards_kick1.x
[unknown] 1853 7268 25.5% -lh5- 1352 Jun 5 10:53 BoardsLib/developer/autodoc/boards.doc
[unknown] 1814 2781 65.2% -lh5- 871d Dec 24 2012 BoardsLib/developer/autodoc/boards.doc.info
[unknown] 954 2471 38.6% -lh5- 30db Jun 7 22:36 BoardsLib/developer/include/asm/libraries/boards.i
[unknown] 106 174 60.9% -lh5- ae35 Jun 5 10:46 BoardsLib/developer/include/asm/lvo/boards_lib.i
[unknown] 322 628 51.3% -lh5- dfbd Jun 5 10:56 BoardsLib/developer/include/c/clib/boards_protos.h
[unknown] 406 1253 32.4% -lh5- c8c2 Jun 5 10:58 BoardsLib/developer/include/c/inline/boards.h
[unknown] 979 2477 39.5% -lh5- 2e7f Jun 7 19:45 BoardsLib/developer/include/c/libraries/boards.h
[unknown] 343 634 54.1% -lh5- d7dc Oct 8 1998 BoardsLib/developer/include/c/NOTE
[unknown] 322 848 38.0% -lh5- 4ddd Jun 5 11:07 BoardsLib/developer/include/c/pragma/boards_lib.h
[unknown] 178 296 60.1% -lh5- 3dae Oct 8 1998 BoardsLib/developer/include/c/proto/boards.h
[unknown] 77 98 78.6% -lh5- f277 Oct 8 1998 BoardsLib/developer/include/e/modules/boards.m
[unknown] 256 398 64.3% -lh5- 44a1 Oct 8 1998 BoardsLib/developer/include/e/modules/libraries/boards.m
[unknown] 164 338 48.5% -lh5- 0941 Jun 5 11:06 BoardsLib/developer/include/fd/boards_lib.fd
[unknown] 11727 23868 49.1% -lh5- 6e6f Jul 26 18:31 BoardsLib/libs/boards.library
[unknown] 8450 17956 47.1% -lh5- 052c Oct 8 2009 BoardsLib/libs/openpci.library
[unknown] 290 637 45.5% -lh5- d68c Jul 26 20:04 BoardsLib.info
---------- ----------- ------- ------- ------ ---------- ------------ ----------
Total 21 files 51931 113807 45.6% Jul 27 19:30
