Here is an index of sites which link to online catalogues of Sydney Parkinson’s paintings. This list is not exhaustive, but will give a good overview of Parkinson’s works in major collections worldwide:
Natural History Museum, London:
Natural History Museum: Endeavour Botanical Illustrations
(by clicking on highlighted regions of the map you can view Parkinson’s illustrations made at that locality)
NHM Images: Sydney Parkinson and Endeavour
British Museum:
Natural History Paintings ex collection of Joseph Banks
National Library of Australia:
Natural History Paintings ex collection of James Lee
Oak Spring Garden Library:
Two Studies of Garden Flowers with Butterfly and Moth
(Select Sydney Parkinson from drop-down menu. As of April 2018 the digital images of these paintings were not available online)
British Library:
Voyages of Captain James Cook: Digital Collections
Australian Art Auction Record:
Sydney Parkinson's Endeavour 