Excel Formula pulling text from another cell

cells 

a1 = apple

a2 = pear

=VLOOKUP($C8,'1. COM SERVICE'!$C$4:$J$25,6)

I need to make '1. COM SERVICE' variable.

VLOOKUP($C8,'a1'!$C$4:$J$25,6) so it would be VLOOKUP($C8,'apple'!$C$4:$J$25,6)

VLOOKUP($C8,'a2'!$C$4:$J$25,6) so it would be VLOOKUP($C8,'pear'!$C$4:$J$25,6)

Thanks for any help.