The ADL book has the RUHRMETALL WOLFSSPINNE 8V2
DRONE HANDLING Speed ACC BODY ARMOR PILOT SENSOR AVA COST
RM Wolfsspinne 8V2 5 1B 1 8(0) 14 4 4 16F 110.000 €
Standard Equipment: Geckofeet, 2 Large Weapon Mounts with 1 Vindicator Minigun each;
Autosofts: Smartsoft, Targeting [Vindicator Minigun] 5
It's not as large, but would satisfy the concept.
Otherwise just use a walker modification on a GMC Bulldog or a Roadmaster and add some heavy weapon mounts...