You can find many brochures and maps at the tourist office. 
Here's an overview:
(the brochures are only available in Dutch)

Castle cycle route Heusden-Zolderfree of charge
BelPop Bonanzafree of charge
Tips for cyclingfree of charge
Limburg Bicycle Map€ 9,50
The Wijers Cycle Map€ 3,00
Mountain bike network Central Limburg€ 4,00
Hiking Maps 
Hiking brochure Eversel-Ubberselfree of charge
Hiking brochure in Valley of the Mangelbeekfree of charge
Hiking brochure mining architecturefree of charge
Hiking brochure slag heap and garden district walkfree of charge
Terril hikefree of charge
Discovery map De Wijersfree of charge
Visitor guide De Wijersfree of charge
Brochure Bear Walkfree of charge
Hiking map Bolderberg-Viversel€ 2,50
Hiking map Platwijers€ 2,50
Hiking map Teuten€ 2,50
Hiking map Bokrijk-Kiewit€ 2,50
Hiking map Kelchterhoef€ 2,50
Hengelhoef hiking map€ 2,50
Hiking map De Maten€ 2,50
Hiking map of the Herkenrode Abbey Site€ 2,50
Hiking map Dauteweyers€ 2,50
Walking box De Wijers€ 17,00
Regional map De Wijers€ 8,00
Regional map Haspengouw€ 8,00
Regional map Kempen Broek€ 8,00
Regional map Hoge Kempen€ 8,00
Regional map Sint Pietersberg€ 8,00
Regional map Vallei vd Zwarte Beek€ 8,00
Regional map of the Meuse Valley€ 8,00
Regional map Bosland€ 8,00
Hiking box Bosland€ 18,00
Walking box: Walking in Limburg€ 34,90
Walking rally TVL€ 4,00
Spotters card De Wijers€ 1,50
Bundle 6 spotters cards De Wijers€ 7,00
De Wijers in a nutshell€ 3,95