Answer:
To get Dustbin Beaver you have to buy a subscription to the Moshi Magazine. Check your email and you should receive a secret code that will get you the Trashy Tulip. When you get the Trashy Tulip, plant it with two other seeds and you should get Dustbin Beaver.
104 Dustbin Beaver The MopTop Tweenybop [Secrets] Ultra Rare: To get Dustbin Beaver you have to subscribe to the Moshi magazine. Check your email and you should have a one-time use, non-sharable code that will get you the Trashy Tulip. Plant the Trashy Tulip with two other seeds and you should get Dustbin Beaver.
See the Related Links for a link to subscribe to the magazine.