Generally, "っぱ" is a euphonic change in the pronunciation of a Japanese word from "は" meaning "のは" or "は of" where は could be "葉 leaf", "歯 tooth", "派 party/faction/school/sect/group", "刃 cutting edge/blade", "波 wave" and etc.
菜{な}っ葉{ぱ}、味噌{みそ}っ歯{ぱ}、反{そ}っ歯{ぱ}、出{で}っ歯{ぱ} are often used with the usage written above including 青{あお}っぱ, 葉{は}っぱ and 杉{すぎ}っぱ.
In addition to the above general explanation, I'll provide supplementary explanation for the two examples: 葉っぱ and 杉っぱ.
As for 葉っぱ, it means "葉 leaf" and we use 葉っぱ often instead of 葉, and according to the above general explanation, 葉っぱ could be written as 葉っ葉.
葉っ葉 is a strange notation, so we write it as 葉っぱ not as 葉っ葉.
葉 and 歯 are both very common words having the same and simple pronunciation.
The reason we use 葉っぱ often instead of 葉 is that we would like to distinguish 葉 from 歯.
As for 杉っぱ, it is probably "杉の葉 cedar leaves" that ordinary Japanese can imagine, but we actually do not see the expression much. The reason is that "杉 cedar" is famous and anyone can understand, but cedar leaves are hard to imagine which part of cedar is actually pointed with the expression of cedar leaves. Things that are difficult to imagine do not have common names, so I think that the expression 杉っぱ or 杉の葉 is not used much.