Can I use my BARCLAY CARD to purchase an iMAC?

We are not Apple, but rather end users like you. For an official answer, contact Apple using the telephone contact for your country shown when you click "contact Support" in the upper right corner of this page, or ask at an Apple retail store if one is near.

Every purchase option has the link shown here:

which takes you to this page:

Apple Financing with Barclaycard Credit Card - Apple

where you can apply.

This is assuming you live in a country where this offer

is available.