If aspx files have no associated designer.vb files available (but they do all have the .vb code behind files)

Fix: if you create a new website (not a web application) then there will not be any designer file and event wiring is through the aspx.
You've most likely made an ASP .NET Web "Site", rather than an ASP .NET "Web Application Project" (only available in VS 2005 SP1 or VS 2008).

With web "sites", there is no .designer.vb file because the code is
dynamically compiled when it is called. You'll notice that in the Page
Directives (in the .aspx source code) that the AutoEventWireUp directive is
set to true, this means that as long as your event handler names are a
combination of the control name, an underscore and the event name, along
with appropriate parameters, the event will automatically "wire up" to the
event handler.