You try other sources like Brothers or Harmons,maybe SoftSeal weatherstripping ?...
Someone must make one..
If not,a hunk of inner tube and sissors can make one,or use a piece of that stick & seal roofing ice dam stuff,or door flashing tape (about the same thing)..or some closed cell foam like a camping/excersize mat,or closed cell foam "sill seal" for building foundations..
I'd be leery of silicone or caulk,some eat metal--butyl rubber gutter seal would be ok,or the 3M urethene stuff they use on a windshield..might need a come-a-long to remove the colum again later though !..