Carl L. Johannessen and Anne Z. Parker, "Maize Ears Sculptured in 12th and 13th Century A.D. India as Indicators of Pre-Columbian Diffusion," Economic Botany 43 , 1989, 164-80, argue that stone carvings of maize ears exist in at least three pre-Columbian Hoysala stone block temples near Mysore, Karnataka state, India. Their article provides 16 photographs of a few of the sculptures in question.
Johannessen has now made three large-scale color photographs available on line at http://darkwing.uoregon.edu/~carljohann , with a brief discussion. These photos reveal considerable detail that is lost in the reduced scale black and white reproductions that appeared in the journal article. His photos are the source of the thumbnails on appearing this site, and are directly linked below:
Also, Yuri Kuchinsky has placed several of the photos appearing in the original Johannessen and Parker Economic Botany article on his website, now at http://www.globalserve.net/~yuku/dif/wmzpix.htm (2 pages, new URL).
Carl L. Johannessen, "Indian Maize in the Twelfth Century [AD]," Nature 14 April 1988, p. 587.
Carl L. Johannessen, "Distribution of Pre-Columbian Maize and Modern Maize Names," in Shue Tuck Wong, ed., Person, Place and Thing: Interpretative and Empirical Essays in Cultural Geography Volume 31 of Geocience and Man . Geoscience Publications, Louisiana State Univ. Dept. of Geography and Anthropology, Baton Rouge, 1992.
Carl L. Johannessen and Anne Z. Parker, "Maize Ears Sculptured in 12th and 13th Century A.D. India as Indicators of Pre-Columbian Diffusion," Economic Botany 43 , 1989, 164-80.
M. Kumar and J.K.S. Sachan, "Antiquity of maize in India", in Maize Genetics Cooperation Newsletter 1993 (vol. 67), p. 98. Click here for text.
M.M. Payak and J.K.S. Sachan, "'Maize' in Somnathpur, an Indian Mediaeval temple," Nature 27 October 1988, pp. 773-4.
M.M. Payak and J.K.S. Sachan, "Maize Ears Not Sculptured in 13th Century Somnathpur Temple in India," Economic Botany 47 (2), 1993, pp. 202-5.
T. Veena and N. Sigamani, "Do Objects in Friezes of Somnathpur Temple (1268 A.D.) in South India Represent Maize Ears?" Current Science 25 Sept. 1991, pp. 395-7. See also fine photo on front cover of issue.
Note that although Sachan's article with Kumar (1993) provides genetic evidence for the antiquity of maize in India, thus independently corroborating the Johannessen and Parker hypothesis, the same Sachan (with Payak, 1988, 1993) curiously remains one of the most outspoken critics of J&P's identification of the sculptures.
The following two items sound pertinent, but I have not yet had a chance to check them out. Andrews is evidently critical of Johannessen and Parker, while Gupta endorses their identification of maize at Somnathpur.
Jean Andrews, article in Geographical Review 83 (1983), 194-204.
Shakti M. Gupta, Plants in Indian Temple Art, 1996.
Photo #1 (.../maize1.JPG) 
Photo #2 (.../maize2.JPG) 
Photo #3. (.../maize13.JPG)