Shovel is the 3rd item unlocked in the Hardware Store. The Hardware Store is unlocked at Level 4, the second commercial building to be unlocked.
Shovel can be produced in 33 minutes in 2 stages without using the Global Trade HQ or a Speed-Up Token. Based on this production time, the simoleons/minute is 4.54. (High-tech Factories and 3-star shops were used for these calculations.)