How i can get Milestone SDK 3.5b redistributable ?.i Would like to integarte Milestone with OnGuard Server and all OnGuard clients.

Please note that what you are asking for is a 9 year old package that has not been maintained since then and Milestone no longer offer any support on this old SDK.

http://download.milestonesys.com/SDK/Milestone_SDK_3.5_Redistributable_Package.msi