We dont know of any christians on Lombok, but my suggestion would be to try and get a recommendation from one of the hotels offering wedding services..
for example
http://www.hotelombak.com/wedding.htmlThere is also some useful info on that link regarding the formalities and documentation needed.
Most of the churches are in Mataram it seems so you may have to go there and have another kind of ceremony in Sekotong afterwards
Or try these (Google is your friend
)
Protestant Churches:
Bethany Mataram Church
+62 370- 625-956
Jl. I Gusti Ketut Jelantik Gosa 23 Mataram
HKBP Mataram Church
+62 370- 632-924
Jl. Gili Air 4 Mataram
Kristen Tuhan Church
+62 370- 621-811
Jl. Ekas 47 Mataram
Masehi Advent H7 Church
+62 370- 638-500
Jl. Kom L Yos Sudarso 16 Mataram
Pantekosta Church
+62 370- 631-219
Jl. Pariwisata 4 Mataram