AIRPORTS: there best alternative would be arriving from Stavanger (Sola) airport.
--Stavanger (2.5h): you can take the shuttle bus from Sola airport to Stavanger. Then, get the NOR-WAY bus (rute 300) in Stavanger and stop in Lyngdal Rom Terminal.
--Kristiansand (2.5h): you can take the airport bus from Kjevik airport to Kristiansand city. Then, get the local AKT bus (A) in Kristiansand and stop at Lyngdal/Farsund/Borhaug.
--Oslo (7h): there is two airports, Gardemoen and Rygge. You should arrive to Oslo city by bus/train and then get the train in Oslo city and stop in Snartemo (NSB) or the bus and stop in Lyngdal (Rute Nr 191).