If I purchased supplies and did not use them all and need to record the value of the leftover supplies on my balance sheet, where do I record it?

You will have2 scenerios

(A) When you bought those supplies either you have expenses them all in the PLS (B) or booked them as supplies stock in Balanse sheet.

If you expense them totally at the time of purchasing, than you need to reverse the un-utilised  portion of supplies and book it in Balance sheet as supplies stock/inventory as assets.

If at the time of purchasing you booked them in BS as Supplies stock/inventory than you only need to expense the used portion in PLS and remaining will automatically appear as asset in BS.

Ending inventory on statement of income (cogs )and on balance sheet as current asset 

If for SALE PURPOSE THEN In Balance Sheet offcourse and your computer software, peach-tree, ERP, Quick-books or SAPS will keep the balance after every transaction you made for sale ... So means you actually don't need to record it with any special entry. It will be showing in your INVENTORY under Current Assets.

If it is for RUNNING EXPENSES THEN you've already expensed it out at the time of purchases. In both cases, all you need to do is keep you INVENTORY/STOCK LIST

Actually, you are answering your own question. Where to record? answer would be, in balance sheet current assets.  When you purchase supplies, the entry would be, DR Supplies or Supplies on hand and Cr Cash or AP. At month end, you can record the used supplies as expense(going to Income statement). Entry: DR Supplies Expense; CR Supplies or Supplies on hand.

if you used parts , you need to physical count your stock

the part consumed recoded as production cost if usage in producation or cost of good sold in commercial entity

if supplies like stationaries or cleaning recoded as period cost

reminaning part not consumed and exit in physical count recored as inventory in current assets

You need to show it as inventory in balance sheet.

As you mentioened  that you need to show them in balance sheet, so the remaining quqntity  will be inventory  and as per what i understood from you question ,it seems that you are applying pweridoc inventory method not prepetual inventory method

The question is where to record the balance value of purchase supplies in balance sheet.??

If you have treated the purchase supplies as an inventry then you can record the balance unused supplies as Inventry assest/Stock in Hand under Current assest in balance sheet.

When you bought those supplies either you have expenses them all in the PLS (B) or booked them as supplies stock in Balanse sheet.

If you expense them totally at the time of purchasing, than you need to reverse the un-utilised  portion of supplies and book it in Balance sheet as supplies stock/inventory as assets.