You can apply for a Permanent Resident Travel Document at the nearest Canadian Embassy, High Commission or Consulate in the country you are currently in. Given how recently you became permanent residents, we would advise explaining why you needed to return to your home country.
Your US visa will not help necessarily. If you enter the US with your visa and take a bus or train to Canada, you will be asked for a visa. Since you are a Permanent Resident, you will likely be directed to the nearest Canadian consulate (or Embassy) in the US to get the travel document. So basically, you still have to get the document.