The drug is derived from the bark of the cinchona tree, native to South America, and by 1856 demand for the drug was surpassing the available supply.

这种药物是从原产于南美洲的金鸡纳树的树皮中提取的。到了1856年，对这种药物的需求已经超过了现有的供应。

youdao

In a tight labour market, demand by employers exceeds the available supply of workers.

在劳动力走俏的市场上，雇主的需求超过工人的供应。

《柯林斯英汉双解大词典》

Since we cannot buy more than is being produced, the additional money only increases the competition for the available supply of products.

既然我们所购买的东西不能超过现有的生产能力，额外增加的货币只能增加对现有产品的竞争。

youdao

So the problem is in the low real wages and low level of demand, not a lack of available supply.

BBC: George Osborne must weigh supply against demand

For instance, homes equipped with solar-power panels could feed unused electricity back into the grid, adding to the total available supply.

FORBES: Magazine Article

Another possible contributor to the large drop in 2011, though, is limited available supply from manufacturers rather than decreased demand from dealers.

FORBES: Auto's Lean Inventory & Shifting Market Share