It all depends on what you mean by "map patronage"? Patronage can cover a lot of things (I found Korshin 1974 to be a useful starting point):
(1) the commissioning of maps and surveys by those in social/political/intellectual authority, usually featuring works of direct importance to themselves, in which case you're potentially looking at all the literature on official mapping activity (e.g. Doel et al. 2006) as well as the literature on art and cartography (I'm thinking of Renaissance mural maps, esp. Fiorani 2005)
(2) the strategy of map makers to use their work to secure the interest
of their superiors and therefore their social and professional advancement - this is a constant theme in my own work on British mapping in the eighteenth and early nineteenth century [Edney 1993, 1994, and parts of 1997] but also see, e.g., Slotten 
(3) structural support for mapping activities through the use of privileges (and copyright) (Pedley 2005), awards [Longitude Prize; Society of Arts prizes], etc. (e.g., Boud 1989 and 1993)
(4) the support of the work of individual scholars and artists -- including map makers -- as an extension of personal patronage, in which case there's a scattered literature (e.g., Barber 1989, Pinto 2011
), but also the need to consider subscription as a modern form of distributed patronage (Bryden 1979, Clapp 1931, Pedley 1979 and 2005)
Hope this helps!
Barber, Peter. 1989. “British Cartography.” In The Age of William III and Mary II: Power, Politics, and Patronage, 1688-1702: A Reference Encyclopedia and Exhibition Catalogue, ed. Robert P. Maccubbin and Martha Hamilton-Phillips, 95-104. Williamsburg, Va.: College of William and Mary for the Grolier Club, New York, and the Folger Shakespeare Library, Washington, D.C.
Boud, R. C. 1989. “Episodes in Cartographic Patronage: The Scottish Agricultural Society and the Coal District Maps, 1834-1847.” Cartographica 26.3-4:59-88.
Boud, R. C. 1993. “Cartographic Patronage and the Highland and Agricultural Society: The Country Geological Premium Competitions, 1835-1847.” Cartographic Journal 30.1:13-29.
Bryden, D. J. 1979. “Cartography by Subscription: An Unsuccessful 18th Century Project to Issue Globes.” Revista da Universidade de Coimbra 27:281-91. Reprinted Publicações do Centro de Estudios de Cartografia Antiga, Série Separatas, 126 [Lisbon: Junta de Investigações Científicas do Ultramar, 1979].
Clapp, S. L. C. 1931. “The Begining of Subscription Publication in the 17th Century.” Modern Philology 29:191-224.
Doel, Ronald E., Tanya J. Levin, and Mason K. Marker. 2006. “Extending Modern Cartography to the Ocean Depths: Military Patronage, Cold War Priorities, and the Heezen–Tharp Mapping Project, 1952–1959.” Journal of Historical Geography 32.3:605-26.
Edney, Matthew H. 1993. “The Patronage of Science and the Creation of Imperial Space: The British Mapping of India, 1799–1843.” Cartographica 30.1:61–67.
Edney, Matthew H. 1994. “Mathematical Cosmography and the Social Ideology of British Cartography, 1780-1820.” Imago Mundi 46:101-16.
Edney, Matthew H. 1997. Mapping an Empire: The Geographical Construction of British India, 1765–1843. Chicago: University of Chicago Press.
Fiorani, Francesca. 2005. The Marvel of Maps: Art, Cartography and Politics in Renaissance Italy. New Haven, Conn.: Yale University Press.
Korshin, Paul J. 1974. “Types of Eighteenth-Century Literary Patronage.” Eighteenth-Century Studies 7.4:453-73.
Pedley, Mary S. 1979. “The Subscription List of the Atlas Universel (1757): A Study in Cartographic Dissemination.” Imago Mundi 31:66-77.
Pedley, Mary Sponberg. 2005. The Commerce of Cartography: Making and Marketing Maps in Eighteenth-Century France and England. Chicago: University of Chicago Press.
Pinto, Karen. 2011. “The Maps Are the Message: Mehmet II's Patronage of an ‘Ottoman Cluster’.” Imago Mundi 63.2:155-79.
Slotten, Hugh Richard. 1994. Patronage, Practice, and the Culture of American Science: Alexander Dallas Bache and the U. S. Coast Survey. Cambridge: Cambridge University Press.