Looks like you need the package from the installation media if you're you're offline (located at D:\sources\sxs
) You could copy this to each machine that you require .NET 3.5 on (so technically you only need the installation media once to get the package) and get each machine to run the command:
Dism.exe /online /enable-feature /featurename:NetFX3 /All /Source:c:\dotnet35 /LimitAccess
There's a guide on MSDN.