If your code is already converted to working VB.Net, why not just leave the calls as they are? The routines are in Microsoft.VisualBasic.dll which is a fully supported part of the .NET framework and will be around as long as .NET is around. Avoid using them in new code if you like, but doing extra work to take them out of existing code seems rather unecessary.
If you haven't yet converted the code, you could choose to buy Artinsoft's VB Upgrade Companion which can do some of the conversions you ask for, as part of the VB6 to VB.Net conversion.
