Fixed Sized Grids

I'd use picture mode for this, then things go just where you put them

\setlength\unitlength{1mm}
\vspace*{0mm}\hspace*{0mm}%
\begin{picture}(210,300)

\put(000,038){\parbox{65mm}{stuff}}
\put(700,038}{\parbox{65mm}{stuff}}
\put(140,038}{\parbox{65mm}{stuff}}

\put(000,000){\parbox{65mm}{stuff}}
\put(700,000}{\parbox{65mm}{stuff}}
\put(140,000}{\parbox{65mm}{stuff}}
....
\end{picture}

You can then move the entire picture mode as a block by changing the \vspace and \hspace values to fit to your existing divisions.

This is a different solution using tabularht package.

You don't have the need to specify any length, since it automatically stretches to the choosen paper size.

\documentclass[10pt]{article}
\usepackage[margin=0.0in]{geometry}
\usepackage{tabularx}
\usepackage[vlines]{tabularht}

\setlength{\parindent}{0pt}

\begin{document}
\begin{tabularhtx}{\paperheight}{\paperwidth}{X|X|X}
\interrowspace{5pt}
example & example & example\\
\interrowfill\hline
\interrowspace{5pt}
example & example & example\\
\interrowfill\hline
\interrowspace{5pt}
example & example & example\\
\interrowfill\hline
\interrowspace{5pt}
example & example & example\\
\interrowfill\hline
\interrowspace{5pt}
example & example & example\\
\interrowfill\hline
\interrowspace{5pt}
example & example & example\\
\interrowfill\hline
\interrowspace{5pt}
example & example & example\\
\interrowfill
\end{tabularhtx}
\end{document} 

Output

I suggest you take a look at the labels package. If I understand you correctly, you should be able to do exactly what you want with it.

Here's a (not so) minimal example, based on texdoc labels.

\documentclass{article}
\usepackage{labels}
    \LabelCols=3% Number of columns of labels per page
    \LabelRows=7% Number of rows of labels per page
    \LeftBorder=1mm% Space added to left border of each label
    \RightBorder=1mm% Space added to right border of each label
    \TopBorder=1mm% Space to leave at top of sheet
    \BottomBorder=1mm% Space to leave at bottom of sheet
\begin{document}
\begin{labels}
Here is one label

Here is another, separated by an empty line.

Here is the third

This one should be on the next line.

This label is very very long, and should thus wrap in the space alloted to one label.
We can also introduce linebreaks \\ by adding \verb+\\+ somewhere

Here's the next label

Here's the last label, because it's time to stop.

\dots

\dots
\end{labels}
\end{document}