Jerry is very correct about Handbook 44. Do be on notice, though, it is a pretty extensive document.

Handbook 44 is written primarily for vendors calibrating large scales (like truck scales). For large scales, the standard allows for abbreviated range testing; meaning it is acceptable to check a scale up to 50% of range. That may not always serve the needs in the best manner.
I think you should be evaluating how you use the scale/balance also. I'm not as sure about scales (typically using 3-4 load cells), but analytical balances (typically with 1 sensor) has a "sweet spot". So if you have a balance with a range of 0-1000 grams, it's optimal operating area is around 50% (500 grams). It will become much less stable as you get closer to 0%, with trying to weigh 10 grams will be challenging (if you are verifying repeatability). If an analytical balance is used for assay measurement in the FDA realm, per USP 41 the minimum weight
must be identified and documented. Not a bad idea to do on any balance, though.
So you should consider qualifying your scale. What is the range of the scale, and what test points do you use it at? Consider what the maximum weight that will be applied to the scale, and the minimum (probably if you tare out a container or something).
Typically, we try to hit around 10%, 50, and 90% of full range (if applicable). Otherwise, you should shoot for something like 0, 25, 50, 75, and 100% of use range. Don't forget to conduct corner load tests.
Mass Standards:
In general, try to purchase several small denomination weights. There is a pretty big difference in moving around 10, 5kg weights and one 50kg weight.

There's a huge difference between 1 500 kg weight and 10 50 kg weights; and so on. You can construct metal carts to transport the weights. If you can stay small, around 20 kg and below per weight, someone should easily be able to lift them. From there up, you will probably want a hoist/pulley system.
Depending on the desired accuracy, Class F weights should be good.
Unless you have a lot of scales, it may not be worth it to do it yourself. There may be a local competent lab to do it for you. However, do recall they may not check it up to full range (per Handbook 44).