Periodicals of the time might be helpful...although pictures of fighting off giant squids are apt to be few and far between. I seem to remember that Harpers Weekly has an online archive of issues dating back 150 years or so.

Try to find illustrations by Édouard Riou of the novels by Jules Verne.

How about Google Books? For Melville, for example, they have full view versions of Moby Dick, Omoo, Typee, and White Jacket, each with several drawings. Another example is Sailing Alone Around the World by Joshua Slocum. Some books list illustrations in the TOC, others you have to scroll through. For inspiration as to titles, and a few included illustrations, try this.

Thanks all...really appreciate the immediate feedback!

You might also like this blog: http://bibliodyssey.blogspot.com/

1800 is very early. Starting from the 1840s, you could check archives of the London Illustrated News for engravings.

Google Rockwell Kent Moby Dick: images.

Kent knew what sailors faced, as he had had a few sailing adventures himself.
His book N by E recounts the tale of a trip he made to Greenland in the 1920s, including shipwreck, with 100 of his woodcuts and beautiful typography.

Dover Publications sells collections of old illustrations for use as clip art. They have several books of whaling/seafaring illustrations. Don't know if the illustrations date back to the 1800s, though. You can order their books online, and larger bookstores often carry some of them.

Home page -- doverpublications.com
Some of their nautical books -- http://store.doverpublications.com/0486437418.html