Hi,I'm Miranda, and I'll be happy to help you with your question.
After researching, the only place I've found an 18-volt HD-DC Coleman Powermate charger for model PMD8146 is on Ebay. The prices range from $34.99-$59.99. Here are a few links to some auctions that are currently going on for this type of charger. All three of these are from the same seller; however, he is offering a $10.00 refund if you have an old charger you want to send in to him.
I hope that answered your question. If you have further questions, please ask. It's been my pleasure helping you. Please remember to rate my answer positively, as rating me is the only way I receive payment/credit for my work. If you would like to request my help in the future, please post your question with "For Miranda Only" at the beginning, and I will respond.