Hi Alamgeer,
Vikram is right . All you need is two LUA Servers .one called LUA1getting its updates directly from Symantec Website and distributing it and the Other called LUA2 should take the Updates from the LUA1 (LUA1 should be described as the Source Server) and distibute it for the Clients .Three Simple Steps will be .
a) Install LUA1 and configure it to get updates from Internet (Symantec)
b)Install LUA2 and configure it to get updates from LUA1
c) Configure your clients via SEPM to get updates from LUA2
Please update this thread and let us know if you are able to achieve your objective .