1998 built new day 1 relic PC, 19 years old in your hands,
gee parts are scarce on things that old. use or new. then or now. but.
buy used parts on ebay
or google the world for them , and bingo.
the IBM service manual and parts list are all over the web, google them.
google all that , seen below for you.
the
bottom is called the bottom pan.
or
05K5482 - Base Cover Assembly (M/ 2626)
what matters is real IBM P/N# only.
there were 3 screen sizes so 3 bottoms,. 12.1" sure
bottom pan is,, 05K5482
seen here 2626 pages ,for free,
https://thinkpads.com/support/hmm/hmm_pdf/390hmm.pdf
first google hit (do it your self find them closer to home?)
EVERY DAY , GOOGLE FINDS MORE OR LESS
FATE WINS.(On used parts for sure)
https://www.impactcomputers.com/05k5482.html