The abstraction of the variations is called the variation parent. The title element of the variation parent names the variations, for example, "Long Sleeve Classic Pocket Tee." Because the parent ASIN is an abstraction, it cannot be purchased, that is, it is not associated with an offer. The following request uses the Offers response group in an ItemLookup of a parent variation.

http://ecs.amazonaws.com/onca/xml?
Service=AWSECommerceService&
AWSAccessKeyId=[AWS Access Key ID]&
Operation=ItemLookup&
ItemId=B00006XYAB&
IdType=ASIN&
MerchantId=All&
Condition=All
ResponseGroup=ItemAttributes,Offers

As you can see in the following response snippet, no offers are returned.

<Item>
  <ASIN>B00006XYAB</ASIN>     <DetailPageURL>http://www.amazon.com/gp/redirect.html%3FASIN=B00006XYAB%26tag=ws%26lcode=xm2%26cID=2025%26ccmID=165953%26location=/o/ASIN/B00006XYAB%253FSubscriptionId=1V9M7E1ZATWETZDS6W82</DetailPageURL>
  <ItemAttributes>
    <Binding>Apparel</Binding>
    <Brand>Eddie Bauer</Brand>
    <Department>mens</Department>
    <FabricType>leather</FabricType>
    <Feature>Cotton.</Feature>
    <Feature>Single chest pocket.</Feature>
    <Feature>Side seamed to prevent twisting.</Feature>
    <Feature>Coverstitched seams add strength.</Feature>
    <ProductGroup>Apparel</ProductGroup>
    <Title>LongSleeve Classic Pocket Tee</Title>
  </ItemAttributes>
  <OfferSummary>
    <TotalNew>0</TotalNew>
    <TotalUsed>0</TotalUsed>
    <TotalCollectible>0</TotalCollectible>
    <TotalRefurbished>0</TotalRefurbished>
  </OfferSummary>
  <Offers>
    <TotalOffers>0</TotalOffers>
    <TotalOfferPages>0</TotalOfferPages>
  </Offers>
</Item>