I found this link that has a list of engines available for sale. Included are the following: (listed by model, brand?, scale)
Cat C-15, ACERT, 1:12
Cat 3208, NZG, 1:10
MTU 12CY Diesel, NZG, 1:15
Cummins K2000E, SBE, 1:18
Cat 3176, UNK, 1:10
DEUTZ BF8L 513, ENC, 1:15
http://www.constructionscalemodels.c...ription=engine
May you find what your after.

- RCT