Probably won't require source as long as the data you want to display is already being returned in the Product Variant sql query e.g.
Code:
<query name="ProductVariants" rowElementName="Variant">
at the top of the package. Just append the value in the Variant template...so something like
Code:
<xsl:value-of select="$vName" /> <xsl:value-of select="ArtNo"/> - <xsl:value-of select="aspdnsf:GetVariantPrice(VariantID, number(HidePriceUntilCart), Price, SalePrice, ExtendedPrice, Points, $pSalesPromptName, $pTaxClassID)" disable-output-escaping="yes" />
as long as ArtNo is a valid field name (or cast field name) in the ProductVariants query