Duncan, an ambassador for Boston Spa-based Martin House, stepped down from the news programme in May after 19 years presenting the show.
Duncan said: “I’ve never been a great follower of fashion but I’ve been fortunate to collect a few designer suits and ties over nearly two decades at Calendar and I think it’s time for some of them to find a place in someone else’s wardrobe.
“They’ve been seen on live TV and spent hours and hours in the studio at television centre in Leeds and now they could be yours.
“I’ve had a long association with Martin House and anything I can do to raise awareness for the incredible work of the hospice while bringing in the odd donation is very worthwhile.”
Martin House cares for babies, children and young people with life-limiting conditions from across West, North and East Yorkshire.
Its care includes planned respite, emergency and symptom control care, end of life care, and bereavement support.
The hospice has nine bedrooms in Martin House, and six in Whitby Lodge, which cares for teenagers and young people.
Bereavement support is offered to families, often for two to three years after their child’s death.
It also offers bereavement support to families whose child had a life-limiting condition but did not have the opportunity to use the hospice, or following a sudden death.
It costs nearly £9 million a year to provide this care, the majority of which comes from voluntary donations and fundraising.
Sunny Allison, retail area manager at Martin House, said: “We’d like to say a huge thank you to Duncan for thinking of Martin House and donating his suits to us to sell in our shops.
“Our charity shops play an important role in helping us to raise fund for the vital care we provide, and we’re always in need of donations of quality pre-loved items like this.”
Find shops at: www.martinhouse.org.uk/shops