Match 2 Values from Combobox on Sheet then populate combobox with 3rd column value

Edit: I see now that I should have worded the subject as "Match 2 values from Combobox TO sheet..." The comboboxes are not on the worksheet itself, they are on a userform and need to match values on a worksheet.

I have a userform that has 3 combobox on it that we use for an inventory.

The first combobox "firstname" has a list of usersfirst names that it pulls from Column C on the worksheet.

Based on what they choose for "firstname" it searches that column and anytime there is a match, it will add the value next to it from Column B to my second combobox called "lastname".

This part all works fine, but this is where I run into a problem.

Based on what is chosen for their firstname and lastname, I need to populate the third combobox "equiptype" with the value that is in Column A, assuming that Column C matches "firstname" and Column B matches "lastname".

This has to be completely dynamic, as users can have more than one piece of equipment, which can change. This way we can choose a piece of equipment the user has without having to guess or refer back to the worksheet.

I can't just match it to their first or last name, because we have multiple users with the same first or the same last names, and we have to have the first and last name separate columns. And each piece of equipment has to be on a different line.

This is how I am populating the firstname and lastname comboboxes if it makes any difference (which works very slick):

Dim myList As New Collection
Dim rngArea As Range
Dim rngCell As Range
Dim vaValues As Variant
Dim choice As String
Set myList = Nothing
Set myList = New Collection

choice = lastname.Value
Set rngArea = Worksheets("Active").Range(Range("B3"), Range("B65536").End(xlUp))

On Error Resume Next
For Each rngCell In rngArea
If choice = rngCell.Value Then
myList.Add rngCell.Offset(0, 1).Value, CStr(rngCell.Offset(0, 1).Value)
End If
Next rngCell
On Error GoTo 0

For Each vaValues In myList
firstname.AddItem vaValues
Next

To try to make things a little clear, here is an example:
Column A (equipment types)
A3- Phone
A4- PC
A5- Air Card
A6- Cell Phone
A7- Headset

Column B (last names)
B3- Smith
B4- Doe
B5- Thompson
B6- Smith
B7- Schmidt

Column C (first names)
C3- Mike
C4- Paul
C5- John
C6- Mike
C7- Mike

So let's say I chose "Mike" for the firstname combobox and "Smith" for the lastname combobox, in the equiptype combobox I now want to see "Phone" and "Cell Phone".

It's this equiptype combobox that is throwing me off. I can't figure out how to get it to match two pieces of criteria, and populate the third combobox.

We have too many equiptypes and too many names to try to sort through what someone has or doesn't have, and it changes so frequently. So seeing just what they have would make the rest of the form so much smoother!

Any help on getting the third dynamic combobox to populate would be great!