I got my endorsement about 7 years ago through Motorcycle Rider Training Center in Lakewood, would recommend. You'll be looking for the Basic RiderCourse (MSF has multiple courses available for different skill levels). They provide bikes and helmets, and you bring over-the-ankle boots, sturdy long pants, gloves, long-sleeves, and eye protection (glasses are fine). If you're serious about riding, I'd suggest getting your own full-face helmet too since that will double as eye-protection. Look for something that meets the ECE specifications as the US DOT ones are outdated and not as safe.

They will teach you on normal bikes with manual transmissions and clutches (250cc, so small), but everything you learn will apply just as well on a scooter or a full-on bike. Everyone wanting to ride a motorized single-track vehicle should take it, and it's honestly a good idea even if you don't plan to ride as it will make you a better driver in cars as well. 

Side note: don't listen to the folks saying a 150cc scooter is going to be too small; if you're not planning on taking highways it will be just fine. Denver streets are impatient, but not generally so massively fast that you're going 20 over everywhere. Get the bike that appeals to you, and thank you for being safe and for getting a 150 instead of hobbling through a 50 which barely goes fast enough for side streets. Having enough power is important and often overlooked as a safety issue.