how to achieve more natural vaginal lubrication?

It is not really possible to boost it. If longer foreplay does not help, there are plenty of different personal lubricants available from the condom rack in your local pharmacy or super market. The water based ones are easy to clean but might evaporate so you will have to top up. The silicone based ones are more expensive but lasts longer.

You do say that it is difficult to find personal lubricants where you live? Saliva is good. Oral sex on you can make you very wet before intercourse. I have also seen olive oil recommended as a lubricant. I suppose that brings new meaning to the term 'Extra Virgin Olive Oil'

The first choice will however be a bought personal lubricant.

Your lubrication is affected by stress, aging and medicines (allergy, cold, antidepressants, birth control etc.). It is also normal for women to fluctuate. It is likely to just return to normal in a few months from now.

Best of luck!

Vaseline works and is cheap and easily available though shouldn't be used with condoms.

My advice is have a look around the kitchen to see what you have that is slippery and without perfumes, etc.
Try anything you have...

An ageing lady who didn't lubricate very well readying herself for her husband chose Vick's mentholated rub, mistaking it in the dark for vaseline...
She reported it added a new dimension to their lovemaking as she couldn't bear to lay still and her husband voted it as the best ever!