There is a lot to take in to get you started. Longshot powder will give you loads at 11/8 oz with plenty of speed, like 1400 fps. You should become familiar with the online Hodgdon reloading data. Longshot is also quite available compared to other powders. You can also order powder on the Hodgdon website but I am pretty sure other mainstream websites also have Longshot.
Powder Valley, Grafs, Precision Reloading, Mid South Shooting Supply, Brownells, Midwayusa, Recobs, and others.
However, Trap does have rules and the max speed for 1 1/8 oz is 1290fps. Someone already mentioned 7.5 being the biggest shot size. That may not be a big deal if you are just shooting informally but you might get kicked off a range if your loads are too hot.
Cheddite primers are pretty available at the same sites that have powder. You will also need a press and an accurate scale that measures in grains. Lyman pocket scale will do the job along with many others. I now use a Noname I found on Amazon for about $16.
Look at the MEC 600 Jr. press. Should be under $300 new.
Data here
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