Well, in effect the cycle~ object allows you to read from a stored cosine function (use a phase offset of 0.75 to get a sine phase), and does high-quality interpolation to give you excellent resolution even though it only uses a 512-sample table. (See MSP Tutorial chapters 1-3.)
But if you want to put a sine wave into a buffer~, here’s a way.
— Pasted Max Patch, click to expand. —
Copy all of the following text. Then, in Max, select New From Clipboard.