You can hear some great funky slap bass lines on just about everything by Level 42. Mark King played 4- and 5-string StingRays on most of the songs on the albums "Guaranteed" and "Forever Now". Some choice Level 42 songs with great slap bass lines are:
"Love Games" (album - "Level 42")
"Sandstorm" (album - "The Early Tapes")
"Mr. Pink" (albums - "The Early Tapes" and "Physical Presence")
"43" (album - "Level 42" self-titled)
"Eyes Waterfalling" (album - "The Pursuit of Accidents")
"Micro Kid" (album - "Standing in the Light")
"Hot Water" (album - True Colours)
"I Sleep On My Heart" and "Dream Crazy" (album - "World Machine")
"If You Were Mine" (album - "Guaranteed")
"Forever Now" (album - "Forever Now")
If you want to pick up a couple of their CDs I recommend "Ultimate Collection" which is a good overview of their material, as well as "Physical Presence" which is one of the funkiest live albums you'll ever hear. You can find these on Amazon.com, but probably not at your local CD store.