There are 3 main repostitories for them
(a) pre 1702 in lib canc (see www.manxnotebook.com/catalog/d245.htm) - on mormon microfilm
(b) within wills
(c) under South or northside sales - there is an index to these in Museum + also on mormon microfim (but when I borrowed a copy it was unreadable - the museum is a reversed white on black copy ) - the contracts are filed with the deeds in Museum and are about the only 'real' item you will get to use.