The themed catalog foldouts were typically supplemental inserts included in the retail box, though for the smaller products that came in plastic blister packaging they may have been the only insert present. I identify the year and the product theme for each.
Busytown
1998
Brochure from 1998. JPEG.
1999
A brochure from 1999. This was extracted from a low-resolution photograph. The quality isn’t great, and it required some distortion correction, but it’s readable. JPEG, 172 KB.
Jim Knopf
2000
The four-page insert from the German 2000 Wooden Railway photo book.
Sky Train
2003
The first generation of Sky Train products. JPEG, 712 KB.
2004
Adds the clock tower, and the battery engine and its accessories. JPEG.
Theodore Tugboat
1998
A brochure from 1998. JPEG, 261 KB.
1999
A brochure from late 1998 or early 1999. Taken from the Theodore Tugboat Wiki. JPEG.
Thomas and Friends
1998
Scan courtesy of BRIO collector artheathen. JPEG, 502 KB.
1999
Scan courtesy of BRIO collector artheathen. JPEG, 486 KB.
Trains of the World
1995
Marks the beginning of the Trains of the World series. JPEG, 1.45 MB.
1996
Adds the Canadian Pacifc. Scan courtesy of BRIO collector artheathen. JPEG, 1.87 MB.
1997
Adds the Flying Scotsman, but drops the LMS, GWR, and LNER engines. Scan courtesy of BRIO collector artheathen. JPEG, 1.12 MB.