Well this sounds after an unofficial announcment of (playable?) Nations.
Anyway , I found this for France:
http://www.marinegarde.de/index4.html
but i think ist a liddle bit to far in history for the game.
This is for 1786-1790 i hink:
http://digitalgallery.nypl.org/nypldigital/dgkeysearchdetail.cfm?strucID=589688&imageID=1236992
http://digitalgallery.nypl.org/nypldigital/dgkeysearchdetail.cfm?strucID=589689&imageID=1236993
http://digitalgallery.nypl.org/nypldigital/dgkeysearchdetail.cfm?strucID=589691&imageID=1236995
And something more napoleonic:
http://www.line-of-battle.de/uniformen
1700+:
http://upload.wikimedia.org/wikipedia/commons/1/15/Officier_de_marine_francais_dessin_allegorique_vers_1700.jpg
http://upload.wikimedia.org/wikipedia/commons/6/68/Grasse%2C_Count_de_%28bust%29%2C_1837_-_NARA_-_512939.tif
Somthing for Spain:
http://upload.wikimedia.org/wikipedia/commons/6/66/Blas_de_Lezo_unknown_author.jpg
Netherlands:
(before 1700) http://commons.wikimedia.org/wiki/File:Portrait_of_Michiel_de_Ruyter_-_Atlas_Blaeu-Van_der_Hem_%28Volume_II%29.jpg
(1784) http://commons.wikimedia.org/wiki/File:Suffen_recevant_une_epee_d_or_de_la_Hollande.jpg
http://commons.wikimedia.org/wiki/File:Daniel-Orme-Duncan-receiving-Surrender-at-Camperdown-jpg.jpg
I hope it helped a liddle bit. i know Wikipedia is not the best port for historical accuracy but it's better than nothing.